<meta name="fuzzy" content="maxDifference=0-1; totalPixels=0-127" />
<style>
body {
    background-image: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 10 10"><g fill="#ccc"><rect width="5" height="5"/><rect x="5" y="5" width="5" height="5"/></g></svg>');
    background-size: 100px 100px;
}

:root {
    --x: black;
}

.box {
    display: inline-block;
    width: 60px;
    height: 60px;
    background-color: #666;
    box-shadow: 3px 3px 3px var(--x);
    margin: 10px 10px;
}
</style>
<p>These two rows should be identical</p>
<div class="box" style="--x: red;"></div>
<div class="box" style="--x: rgb(0, 255, 0);"></div>
<div class="box" style="--x: blue;"></div>
<div class="box" style="--x: rgba(255, 0, 0, 0.6);"></div>
<div class="box" style="--x: rgba(0, 255, 0, 0.6);"></div>
<div class="box" style="--x: rgba(0, 0, 255, 0.6);"></div>
<br>
<div class="box" style="--x: color(srgb 1 0 0);"></div>
<div class="box" style="--x: color(srgb 0 1 0);"></div>
<div class="box" style="--x: color(srgb 0 0 1);"></div>
<div class="box" style="--x: color(srgb 1 0 0 / 0.6);"></div>
<div class="box" style="--x: color(srgb 0 1 0 / 0.6);"></div>
<div class="box" style="--x: color(srgb 0 0 1 / 0.6);"></div>