LayoutTests/fast/loader/user-stylesheet-data-url.html

<!DOCTYPE html>
<html>
<head>
<title>User style sheet from a data: URL</title>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
</head>
<body>
<script>
function utf8ToBase64(string) {
    return btoa(String.fromCharCode(...new TextEncoder().encode(string)));
}

function testUserStyleSheet(location, expected, description) {
    test(() => {
        testRunner.setUserStyleSheetLocation(location);
        const value = getComputedStyle(document.body).getPropertyValue("--test");
        testRunner.setUserStyleSheetLocation("");
        assert_equals(value, expected);
    }, description);
}

testRunner.setUserStyleSheetEnabled(true);

testUserStyleSheet(`data:TEXT/CSS;CHARSET=UTF-8;BASE64,${btoa("body{--test:uppercase}")}`, "uppercase", "Uppercase media type and base64 indicator");
testUserStyleSheet(`data:text/css;base64,${btoa("body{--test:no-charset}")}`, "no-charset", "Base64 without a charset parameter");
testUserStyleSheet(`data:text/css,${encodeURIComponent("body{--test:percent-encoded}")}`, "percent-encoded", "Percent-encoded");
testUserStyleSheet(`data:,${encodeURIComponent("body{--test:no-media-type}")}`, "no-media-type", "No media type");
testUserStyleSheet(`data:text/css;charset=utf-8;base64,${btoa("body{--test:fragment}")}#fragment`, "fragment", "Fragment");
testUserStyleSheet(`data:text/css;charset=utf-8;base64,${utf8ToBase64("body{--test:\u00E9}")}`, "\u00E9", "UTF-8");
testUserStyleSheet(`data:text/css;charset=iso-8859-1;base64,${btoa("body{--test:\u00E9}")}`, "\u00E9", "Non-UTF-8 charset parameter");
</script>
</body>
</html>