css/cssom/preferred-stylesheet-order.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/cssom/#add-a-css-style-sheet">
<link rel="help" href="https://drafts.csswg.org/cssom/#create-a-css-style-sheet">
<link rel="help" href="https://html.spec.whatwg.org/#update-a-style-block">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="t1">This text should be green</div>
<script>
function createStyleElement(text, title) {
    var elm = document.createElement("style");
    elm.setAttribute("title", title);
    elm.appendChild(document.createTextNode(text));
    return elm;
}

test(function() {
    document.head.appendChild(createStyleElement("#t1 {color:green}", "preferred"));
    document.head.appendChild(createStyleElement("#t1 {color:red}", "notpreferred"));

    assert_equals(getComputedStyle(t1).color, "rgb(0, 128, 0)");
}, "Preferred stylesheet where insertion order is reversed tree order");
</script>