css/css-cascade/layer-vs-inline-style.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-cascade-5/#cascade-sort">
<link rel="author" title="Xiaocheng Hu" href="mailto:xiaochengh@chromium.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#target, #reference {
  width: 100px;
  height: 100px;
}

#reference {
  background-color: green;
}
</style>

<div id="target"></div>
<div id="reference"></div>

<script>
// In all tests, #target should have green background color, same as #reference

const testCases = [
  {
    title: 'Normal inline style > normal layered style',
    style: '@layer { #target { background-color: red; }}',
    inlineStyle: 'background-color: green'
  },
  {
    title: 'Normal inline style < important layered style',
    style: '@layer { #target { background-color: green !important; }}',
    inlineStyle: 'background-color: red'
  },
  {
    title: 'Important inline style > normal layered style',
    style: '@layer { #target { background-color: red; }}',
    inlineStyle: 'background-color: green !important'
  },
  {
    title: 'Important inline style > important layered style',
    style: '@layer { #target { background-color: red !important; }}',
    inlineStyle: 'background-color: green !important'
  },
];

for (let testCase of testCases) {
  var documentStyle = document.createElement('style');
  documentStyle.appendChild(document.createTextNode(testCase['style']));
  document.head.appendChild(documentStyle);

  target.style = testCase['inlineStyle'];

  test(function () {
    assert_equals(getComputedStyle(target).backgroundColor,
                  getComputedStyle(reference).backgroundColor);
  }, testCase['title']);

  documentStyle.remove();
}
</script>