diff --git a/LayoutTests/imported/w3c/ChangeLog b/LayoutTests/imported/w3c/ChangeLog
index e4b87cc..5df7c51 100644
--- a/LayoutTests/imported/w3c/ChangeLog
+++ b/LayoutTests/imported/w3c/ChangeLog
@@ -1,5 +1,17 @@
 2021-02-27  Antoine Quint  <graouts@webkit.org>
 
+        border-image-slice blending does not account for the fill keyword
+        https://bugs.webkit.org/show_bug.cgi?id=222513
+
+        Reviewed by Antti Koivisto.
+
+        Pass an extra 96 WPT tests for border-image-slice.
+
+        * web-platform-tests/css/css-backgrounds/animations/border-image-slice-composition-expected.txt:
+        * web-platform-tests/css/css-backgrounds/animations/border-image-slice-interpolation-expected.txt:
+
+2021-02-27  Antoine Quint  <graouts@webkit.org>
+
         Improve blending of LengthBox values
         https://bugs.webkit.org/show_bug.cgi?id=222512
 
diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-composition-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-composition-expected.txt
index b5f271c..d87c5bc 100644
--- a/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-composition-expected.txt
+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-composition-expected.txt
@@ -41,13 +41,13 @@
 FAIL Compositing: property <border-image-slice> underlying [10% 20] from add [90% 80] to replace [0% 0 0% 0] at (0.75) should be [25% 25] assert_equals: expected "25 % 25 " but got "22.5 % 20 "
 PASS Compositing: property <border-image-slice> underlying [10% 20] from add [90% 80] to replace [0% 0 0% 0] at (1) should be [0% 0]
 PASS Compositing: property <border-image-slice> underlying [10% 20] from add [90% 80] to replace [0% 0 0% 0] at (1.25) should be [0% 0]
-FAIL Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (-0.25) should be [100% 150%] assert_equals: expected "100 % 150 % " but got "75 % 125 % "
+PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (-0.25) should be [100% 150%]
 PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0) should be [100% 150%]
-FAIL Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0.25) should be [100% 150%] assert_equals: expected "100 % 150 % " but got "125 % 175 % "
-FAIL Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0.5) should be [200% 250% fill] assert_equals: expected "200 % 250 % fill " but got "150 % 200 % "
-FAIL Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0.75) should be [200% 250% fill] assert_equals: expected "200 % 250 % fill " but got "175 % 225 % "
-FAIL Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (1) should be [200% 250% fill] assert_equals: expected "200 % 250 % fill " but got "200 % 250 % "
-FAIL Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (1.25) should be [200% 250% fill] assert_equals: expected "200 % 250 % fill " but got "225 % 275 % "
+PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0.25) should be [100% 150%]
+PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0.5) should be [200% 250% fill]
+PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (0.75) should be [200% 250% fill]
+PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (1) should be [200% 250% fill]
+PASS Compositing: property <border-image-slice> underlying [10 20] from add [100% 150%] to add [200% 250% fill] at (1.25) should be [200% 250% fill]
 PASS Compositing: property <border-image-slice> underlying [10 20] from add [100 150%] to add [200% 250] at (-0.25) should be [100 150%]
 PASS Compositing: property <border-image-slice> underlying [10 20] from add [100 150%] to add [200% 250] at (0) should be [100 150%]
 PASS Compositing: property <border-image-slice> underlying [10 20] from add [100 150%] to add [200% 250] at (0.25) should be [100 150%]
diff --git a/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-interpolation-expected.txt b/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-interpolation-expected.txt
index 9cdd678..154f7101 100644
--- a/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-interpolation-expected.txt
+++ b/LayoutTests/imported/w3c/web-platform-tests/css/css-backgrounds/animations/border-image-slice-interpolation-expected.txt
@@ -181,20 +181,20 @@
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.6) should be [24 34 44 54 fill]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1) should be [40 50 60 70 fill]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1.5) should be [60 70 80 90 fill]
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (-0.5) should be [0 0 0 10 fill] assert_equals: expected "0 0 0 10 fill " but got "0 0 0 10 "
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0) should be [0 10 20 30 fill] assert_equals: expected "0 10 20 30 fill " but got "0 10 20 30 "
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.3) should be [12 22 32 42 fill] assert_equals: expected "12 22 32 42 fill " but got "12 22 32 42 "
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.5) should be [20 30 40 50 fill] assert_equals: expected "20 30 40 50 fill " but got "20 30 40 50 "
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.6) should be [24 34 44 54 fill] assert_equals: expected "24 34 44 54 fill " but got "24 34 44 54 "
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1) should be [40 50 60 70 fill] assert_equals: expected "40 50 60 70 fill " but got "40 50 60 70 "
-FAIL CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1.5) should be [60 70 80 90 fill] assert_equals: expected "60 70 80 90 fill " but got "60 70 80 90 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (-0.5) should be [0 0 0 10 fill] assert_equals: expected "0 0 0 10 fill " but got "0 0 0 10 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0) should be [0 10 20 30 fill] assert_equals: expected "0 10 20 30 fill " but got "0 10 20 30 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.3) should be [12 22 32 42 fill] assert_equals: expected "12 22 32 42 fill " but got "12 22 32 42 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.5) should be [20 30 40 50 fill] assert_equals: expected "20 30 40 50 fill " but got "20 30 40 50 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.6) should be [24 34 44 54 fill] assert_equals: expected "24 34 44 54 fill " but got "24 34 44 54 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1) should be [40 50 60 70 fill] assert_equals: expected "40 50 60 70 fill " but got "40 50 60 70 "
-FAIL Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1.5) should be [60 70 80 90 fill] assert_equals: expected "60 70 80 90 fill " but got "60 70 80 90 "
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (-0.5) should be [0 0 0 10 fill]
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0) should be [0 10 20 30 fill]
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.3) should be [12 22 32 42 fill]
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.5) should be [20 30 40 50 fill]
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.6) should be [24 34 44 54 fill]
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1) should be [40 50 60 70 fill]
+PASS CSS Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1.5) should be [60 70 80 90 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (-0.5) should be [0 0 0 10 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0) should be [0 10 20 30 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.3) should be [12 22 32 42 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.5) should be [20 30 40 50 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (0.6) should be [24 34 44 54 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1) should be [40 50 60 70 fill]
+PASS Web Animations: property <border-image-slice> from [0 10 20 30 fill] to [40 50 60 70 fill] at (1.5) should be [60 70 80 90 fill]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (-0.5) should be [0% 0 0% 10 fill]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0) should be [0% 10 20% 30 fill]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.3) should be [12% 22 32% 42 fill]
@@ -209,48 +209,48 @@
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.6) should be [24% 34 44% 54 fill]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1) should be [40% 50 60% 70 fill]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1.5) should be [60% 70 80% 90 fill]
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (-0.5) should be [0% 0 0% 10 fill] assert_equals: expected "0 % 0 0 % 10 fill " but got "0 % 0 0 % 10 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "0 % 10 20 % 30 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.3) should be [12% 22 32% 42 fill] assert_equals: expected "12 % 22 32 % 42 fill " but got "12 % 22 32 % 42 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.5) should be [20% 30 40% 50 fill] assert_equals: expected "20 % 30 40 % 50 fill " but got "20 % 30 40 % 50 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.6) should be [24% 34 44% 54 fill] assert_equals: expected "24 % 34 44 % 54 fill " but got "24 % 34 44 % 54 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1) should be [40% 50 60% 70 fill] assert_equals: expected "40 % 50 60 % 70 fill " but got "40 % 50 60 % 70 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1.5) should be [60% 70 80% 90 fill] assert_equals: expected "60 % 70 80 % 90 fill " but got "60 % 70 80 % 90 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (-0.5) should be [0% 0 0% 10 fill] assert_equals: expected "0 % 0 0 % 10 fill " but got "0 % 0 0 % 10 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "0 % 10 20 % 30 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.3) should be [12% 22 32% 42 fill] assert_equals: expected "12 % 22 32 % 42 fill " but got "12 % 22 32 % 42 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.5) should be [20% 30 40% 50 fill] assert_equals: expected "20 % 30 40 % 50 fill " but got "20 % 30 40 % 50 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.6) should be [24% 34 44% 54 fill] assert_equals: expected "24 % 34 44 % 54 fill " but got "24 % 34 44 % 54 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1) should be [40% 50 60% 70 fill] assert_equals: expected "40 % 50 60 % 70 fill " but got "40 % 50 60 % 70 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1.5) should be [60% 70 80% 90 fill] assert_equals: expected "60 % 70 80 % 90 fill " but got "60 % 70 80 % 90 "
-FAIL CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [50%] assert_equals: expected "50 % " but got "0 % "
-FAIL CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0) should be [50%] assert_equals: expected "50 % " but got "0 % "
-FAIL CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [50%] assert_equals: expected "50 % " but got "15 % "
-FAIL CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%] assert_equals: expected "50 % " but got "25 % "
-FAIL CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%] assert_equals: expected "50 % " but got "30 % "
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (-0.5) should be [0% 0 0% 10 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0) should be [0% 10 20% 30 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.3) should be [12% 22 32% 42 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.5) should be [20% 30 40% 50 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.6) should be [24% 34 44% 54 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1) should be [40% 50 60% 70 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1.5) should be [60% 70 80% 90 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (-0.5) should be [0% 0 0% 10 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0) should be [0% 10 20% 30 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.3) should be [12% 22 32% 42 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.5) should be [20% 30 40% 50 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (0.6) should be [24% 34 44% 54 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1) should be [40% 50 60% 70 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70 fill] at (1.5) should be [60% 70 80% 90 fill]
+PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [50%]
+PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0) should be [50%]
+PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [50%]
+PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%]
+PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%]
 PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (1) should be [50%]
-FAIL CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%] assert_equals: expected "50 % " but got "75 % "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [50%] assert_equals: expected "50 % " but got "0 % "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0) should be [50%] assert_equals: expected "50 % " but got "0 % "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [50%] assert_equals: expected "50 % " but got "15 % "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%] assert_equals: expected "50 % " but got "25 % "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%] assert_equals: expected "50 % " but got "30 % "
+PASS CSS Transitions: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [50%]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0) should be [50%]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [50%]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (1) should be [50%]
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%] assert_equals: expected "50 % " but got "75 % "
-FAIL CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [0% fill] assert_equals: expected "0 % fill " but got "0 % "
-FAIL CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0) should be [0% fill] assert_equals: expected "0 % fill " but got "0 % "
-FAIL CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [0% fill] assert_equals: expected "0 % fill " but got "15 % "
-FAIL CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%] assert_equals: expected "50 % " but got "25 % "
-FAIL CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%] assert_equals: expected "50 % " but got "30 % "
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%]
+PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [0% fill]
+PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0) should be [0% fill]
+PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [0% fill]
+PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%]
+PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%]
 PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (1) should be [50%]
-FAIL CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%] assert_equals: expected "50 % " but got "75 % "
-FAIL Web Animations: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [0% fill] assert_equals: expected "0 % fill " but got "0 % "
-FAIL Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0) should be [0% fill] assert_equals: expected "0 % fill " but got "0 % "
-FAIL Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [0% fill] assert_equals: expected "0 % fill " but got "15 % "
-FAIL Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%] assert_equals: expected "50 % " but got "25 % "
-FAIL Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%] assert_equals: expected "50 % " but got "30 % "
+PASS CSS Animations: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%]
+PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (-0.3) should be [0% fill]
+PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0) should be [0% fill]
+PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0.3) should be [0% fill]
+PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0.5) should be [50%]
+PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (0.6) should be [50%]
 PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (1) should be [50%]
-FAIL Web Animations: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%] assert_equals: expected "50 % " but got "75 % "
+PASS Web Animations: property <border-image-slice> from [0% fill] to [50%] at (1.5) should be [50%]
 PASS CSS Transitions: property <border-image-slice> from [50%] to [100] at (-0.3) should be [100]
 PASS CSS Transitions: property <border-image-slice> from [50%] to [100] at (0) should be [100]
 PASS CSS Transitions: property <border-image-slice> from [50%] to [100] at (0.3) should be [100]
@@ -293,48 +293,48 @@
 PASS CSS Transitions with transition: all: property <border-image-slice> from [50% fill] to [100 fill] at (0.6) should be [100 fill]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [50% fill] to [100 fill] at (1) should be [100 fill]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [50% fill] to [100 fill] at (1.5) should be [100 fill]
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (-0.3) should be [50% fill] assert_equals: expected "50 % fill " but got "50 % "
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0) should be [50% fill] assert_equals: expected "50 % fill " but got "50 % "
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.3) should be [50% fill] assert_equals: expected "50 % fill " but got "50 % "
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.5) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.6) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1.5) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (-0.3) should be [50% fill] assert_equals: expected "50 % fill " but got "50 % "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0) should be [50% fill] assert_equals: expected "50 % fill " but got "50 % "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.3) should be [50% fill] assert_equals: expected "50 % fill " but got "50 % "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.5) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.6) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1.5) should be [100 fill] assert_equals: expected "100 fill " but got "100 "
-FAIL CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "0 % 0 8 % 18 "
-FAIL CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "0 % 10 20 % 30 "
-FAIL CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "12 % 22 32 % 42 "
-FAIL CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "20 % 30 40 % 50 "
-FAIL CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "24 % 34 44 % 54 "
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (-0.3) should be [50% fill]
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0) should be [50% fill]
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.3) should be [50% fill]
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.5) should be [100 fill]
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.6) should be [100 fill]
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1) should be [100 fill]
+PASS CSS Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1.5) should be [100 fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (-0.3) should be [50% fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0) should be [50% fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.3) should be [50% fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.5) should be [100 fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (0.6) should be [100 fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1) should be [100 fill]
+PASS Web Animations: property <border-image-slice> from [50% fill] to [100 fill] at (1.5) should be [100 fill]
+PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [40% 50 60% 70]
+PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [40% 50 60% 70]
+PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [40% 50 60% 70]
+PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70]
+PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1) should be [40% 50 60% 70]
-FAIL CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "60 % 70 80 % 90 "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "0 % 0 8 % 18 "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "0 % 10 20 % 30 "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "12 % 22 32 % 42 "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "20 % 30 40 % 50 "
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "24 % 34 44 % 54 "
+PASS CSS Transitions: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [40% 50 60% 70]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [40% 50 60% 70]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [40% 50 60% 70]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70]
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1) should be [40% 50 60% 70]
-FAIL CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "60 % 70 80 % 90 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "0 % 0 8 % 18 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "0 % 10 20 % 30 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "12 % 22 32 % 42 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "20 % 30 40 % 50 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "24 % 34 44 % 54 "
+PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [0% 10 20% 30 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [0% 10 20% 30 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [0% 10 20% 30 fill]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70]
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70]
 PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1) should be [40% 50 60% 70]
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "60 % 70 80 % 90 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "0 % 0 8 % 18 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "0 % 10 20 % 30 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [0% 10 20% 30 fill] assert_equals: expected "0 % 10 20 % 30 fill " but got "12 % 22 32 % 42 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "20 % 30 40 % 50 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "24 % 34 44 % 54 "
+PASS CSS Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (-0.3) should be [0% 10 20% 30 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0) should be [0% 10 20% 30 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.3) should be [0% 10 20% 30 fill]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.5) should be [40% 50 60% 70]
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (0.6) should be [40% 50 60% 70]
 PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1) should be [40% 50 60% 70]
-FAIL Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70] assert_equals: expected "40 % 50 60 % 70 " but got "60 % 70 80 % 90 "
+PASS Web Animations: property <border-image-slice> from [0% 10 20% 30 fill] to [40% 50 60% 70] at (1.5) should be [40% 50 60% 70]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (-0.3) should be [40 50 60% 70]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0) should be [40 50 60% 70]
 PASS CSS Transitions: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.3) should be [40 50 60% 70]
@@ -349,16 +349,16 @@
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.6) should be [40 50 60% 70]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (1) should be [40 50 60% 70]
 PASS CSS Transitions with transition: all: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (1.5) should be [40 50 60% 70]
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (-0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 "
-FAIL CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 "
+FAIL CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (-0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 fill "
+FAIL CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 fill "
+FAIL CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 fill "
 PASS CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.5) should be [40 50 60% 70]
 PASS CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.6) should be [40 50 60% 70]
 PASS CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (1) should be [40 50 60% 70]
 PASS CSS Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (1.5) should be [40 50 60% 70]
-FAIL Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (-0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 "
-FAIL Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 "
+FAIL Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (-0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 fill "
+FAIL Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 fill "
+FAIL Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.3) should be [0% 10 20 30 fill] assert_equals: expected "0 % 10 20 30 fill " but got "0 10 20 30 fill "
 PASS Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.5) should be [40 50 60% 70]
 PASS Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (0.6) should be [40 50 60% 70]
 PASS Web Animations: property <border-image-slice> from [0% 10 20 30 fill] to [40 50 60% 70] at (1) should be [40 50 60% 70]
diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 9a9634b..b69cd26 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,5 +1,34 @@
 2021-02-27  Antoine Quint  <graouts@webkit.org>
 
+        border-image-slice blending does not account for the fill keyword
+        https://bugs.webkit.org/show_bug.cgi?id=222513
+
+        Reviewed by Antti Koivisto.
+
+        The border-image-slice CSS property allows for the "fill" keyword on top of the four values defining the slices.
+        The presence of this keyword is stored as a bool flag on the NinePieceImage returned by RenderStyle::borderImage(),
+        while the four slices values are stored as a separate LengthBox on that NinePieceImage. So as we blend the
+        border-image-slice property using the LengthBoxPropertyWrapper, we only account for the four slices values.
+
+        In order to account for the "fill" keyword, we use an OptionSet instead of a single flag to represent different blending
+        options for CSS properties represented by a LengthBox. This allows us to now indicate that a given property,
+        namely border-image-slice, supports the "fill" keyword.
+
+        If this "fill" keyword flag is set, we force discrete interpolation in the case where the from and to blend values
+        don't have the same value for "fill". Then, as we blend, we set the "fill" keyword to match the from and to values.
+
+        To do this, we add a new RenderStyle::setBorderImageSliceFill() property since the NinePieceImage returned by
+        RenderStyle::borderImage() is marked const.
+
+        * animation/CSSPropertyAnimation.cpp:
+        (WebCore::LengthBoxPropertyWrapper::LengthBoxPropertyWrapper):
+        (WebCore::CSSPropertyAnimationWrapperMap::CSSPropertyAnimationWrapperMap):
+        * rendering/style/RenderStyle.cpp:
+        (WebCore::RenderStyle::setBorderImageSliceFill):
+        * rendering/style/RenderStyle.h:
+
+2021-02-27  Antoine Quint  <graouts@webkit.org>
+
         Improve blending of LengthBox values
         https://bugs.webkit.org/show_bug.cgi?id=222512
 
diff --git a/Source/WebCore/animation/CSSPropertyAnimation.cpp b/Source/WebCore/animation/CSSPropertyAnimation.cpp
index 92e97a0..a56e22f 100644
--- a/Source/WebCore/animation/CSSPropertyAnimation.cpp
+++ b/Source/WebCore/animation/CSSPropertyAnimation.cpp
@@ -736,16 +736,22 @@
 class LengthBoxPropertyWrapper : public PropertyWrapperGetter<const LengthBox&> {
     WTF_MAKE_FAST_ALLOCATED;
 public:
-    enum class IsLengthPercentage { Yes, No };
-    LengthBoxPropertyWrapper(CSSPropertyID prop, const LengthBox& (RenderStyle::*getter)() const, void (RenderStyle::*setter)(LengthBox&&), IsLengthPercentage isLengthPercentage = IsLengthPercentage::No)
+    enum class Flags {
+        IsLengthPercentage  = 1 << 0,
+        UsesFillKeyword     = 1 << 1,
+    };
+    LengthBoxPropertyWrapper(CSSPropertyID prop, const LengthBox& (RenderStyle::*getter)() const, void (RenderStyle::*setter)(LengthBox&&), OptionSet<Flags> flags = { })
         : PropertyWrapperGetter<const LengthBox&>(prop, getter)
         , m_setter(setter)
-        , m_isLengthPercentage(isLengthPercentage)
+        , m_flags(flags)
     {
     }
 
     bool canInterpolate(const RenderStyle* a, const RenderStyle* b) const override
     {
+        if (m_flags.contains(Flags::UsesFillKeyword) && a->borderImage().fill() != b->borderImage().fill())
+            return false;
+
         auto canInterpolateBetweenLengths = [&](const Length& a, const Length& b) -> bool {
             if (a.type() == b.type() || a.isZero() || b.isZero())
                 return true;
@@ -754,7 +760,7 @@
             // between a <length> and a <percentage>, but exclude animating between a <number> and either
             // a <length> or <percentage>. We can use Length::isRelative() to determine whether we are
             // dealing with a <number> as opposed to a <length> or <percentage>.
-            if (m_isLengthPercentage == IsLengthPercentage::Yes)
+            if (m_flags.contains(Flags::IsLengthPercentage))
                 return a.isRelative() == b.isRelative();
 
             return false;
@@ -770,8 +776,12 @@
 
     void blend(const CSSPropertyBlendingClient* anim, RenderStyle* dst, const RenderStyle* a, const RenderStyle* b, double progress) const override
     {
-        if (!canInterpolate(a, b))
+        if (!canInterpolate(a, b)) {
             progress = progress < 0.5 ? 0 : 1;
+            if (m_flags.contains(Flags::UsesFillKeyword))
+                dst->setBorderImageSliceFill((progress ? b : a)->borderImage().fill());
+        } else if (m_flags.contains(Flags::UsesFillKeyword))
+            dst->setBorderImageSliceFill(a->borderImage().fill());
         (dst->*m_setter)(blendFunc(anim, (a->*PropertyWrapperGetter<const LengthBox&>::m_getter)(), (b->*PropertyWrapperGetter<const LengthBox&>::m_getter)(), progress));
     }
 
@@ -779,7 +789,7 @@
     void (RenderStyle::*m_setter)(LengthBox&&);
 
 private:
-    IsLengthPercentage m_isLengthPercentage;
+    OptionSet<Flags> m_flags;
 };
 
 class PropertyWrapperClipPath : public RefCountedPropertyWrapper<ClipPathOperation> {
@@ -1843,8 +1853,8 @@
         new StyleImagePropertyWrapper(CSSPropertyWebkitMaskImage, &RenderStyle::maskImage, &RenderStyle::setMaskImage),
 
         new StyleImagePropertyWrapper(CSSPropertyBorderImageSource, &RenderStyle::borderImageSource, &RenderStyle::setBorderImageSource),
-        new LengthBoxPropertyWrapper(CSSPropertyBorderImageSlice, &RenderStyle::borderImageSlices, &RenderStyle::setBorderImageSlices),
-        new LengthBoxPropertyWrapper(CSSPropertyBorderImageWidth, &RenderStyle::borderImageWidth, &RenderStyle::setBorderImageWidth, LengthBoxPropertyWrapper::IsLengthPercentage::Yes),
+        new LengthBoxPropertyWrapper(CSSPropertyBorderImageSlice, &RenderStyle::borderImageSlices, &RenderStyle::setBorderImageSlices, { LengthBoxPropertyWrapper::Flags::UsesFillKeyword }),
+        new LengthBoxPropertyWrapper(CSSPropertyBorderImageWidth, &RenderStyle::borderImageWidth, &RenderStyle::setBorderImageWidth, { LengthBoxPropertyWrapper::Flags::IsLengthPercentage }),
         new LengthBoxPropertyWrapper(CSSPropertyBorderImageOutset, &RenderStyle::borderImageOutset, &RenderStyle::setBorderImageOutset),
 
         new StyleImagePropertyWrapper(CSSPropertyWebkitMaskBoxImageSource, &RenderStyle::maskBoxImageSource, &RenderStyle::setMaskBoxImageSource),
diff --git a/Source/WebCore/rendering/style/RenderStyle.cpp b/Source/WebCore/rendering/style/RenderStyle.cpp
index 2aa7cea..dff6243 100644
--- a/Source/WebCore/rendering/style/RenderStyle.cpp
+++ b/Source/WebCore/rendering/style/RenderStyle.cpp
@@ -2310,6 +2310,13 @@
     m_surroundData.access().border.m_image.setImage(WTFMove(image));
 }
 
+void RenderStyle::setBorderImageSliceFill(bool fill)
+{
+    if (m_surroundData->border.m_image.fill() == fill)
+        return;
+    m_surroundData.access().border.m_image.setFill(fill);
+}
+
 void RenderStyle::setBorderImageSlices(LengthBox&& slices)
 {
     if (m_surroundData->border.m_image.imageSlices() == slices)
diff --git a/Source/WebCore/rendering/style/RenderStyle.h b/Source/WebCore/rendering/style/RenderStyle.h
index 35937de..ad840cf 100644
--- a/Source/WebCore/rendering/style/RenderStyle.h
+++ b/Source/WebCore/rendering/style/RenderStyle.h
@@ -884,6 +884,7 @@
     
     void setBorderImage(const NinePieceImage& b) { SET_VAR(m_surroundData, border.m_image, b); }
     void setBorderImageSource(RefPtr<StyleImage>&&);
+    void setBorderImageSliceFill(bool);
     void setBorderImageSlices(LengthBox&&);
     void setBorderImageWidth(LengthBox&&);
     void setBorderImageOutset(LengthBox&&);