Source/WebCore/Modules/modern-media-controls/controls/ios-inline-media-controls.css

/* Volume slider */

.media-controls.inline.ios:not(.audio) {
    background-color: rgba(0, 0, 0, 0.55);
}

.media-controls.inline.ios:not(.audio):is(:empty, .faded) {
    background-color: transparent;
}

.media-controls.inline.ios:not(.audio) * {
    --primary-glyph-color: white;
    --secondary-glyph-color: rgba(255, 255, 255, 0.75);
}

.media-controls.inline.ios:not(.audio) > .controls-bar:is(.top-left, .top-right) {
    height: 19px;
}

.media-controls.inline.ios:not(.audio) > .controls-bar.center {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}