css/css-cascade/layer-scroll-timeline-override.html

<!DOCTYPE html>
<title>Resolving @scroll-timeline name conflicts with cascade layers</title>
<link rel="help" href="https://drafts.csswg.org/css-cascade-5/#layering">
<link rel="author" href="mailto:xiaochengh@chromium.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/web-animations/testcommon.js"></script>
<style>
#scroller {
  overflow: scroll;
  width: 100px;
  height: 100px;
}

#scroller div {
  height: 200px;
}

@keyframes expand {
  from { width: 100px; }
  to { width: 200px; }
}

#target, #reference {
  height: 100px;
}

#reference {
  width: 150px;
}

#target {
  animation: expand 10s linear;
  height: 100px;
}
</style>

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

<script>
// In all tests, width of #target should be 150px, same as #reference

const testCases = [
  {
    title: '@scroll-timeline unlayered overrides layered',
    style: `
      #target {
        animation-timeline: timeline;
      }

      @scroll-timeline timeline {
        source: selector(#scroller);
        start: 0px;
        end: 50px;
      }

      @layer {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 100px;
        }
      }
    `
  },

  {
    title: '@scroll-timeline override between layers',
    style: `
      @layer base, override;

      #target {
        animation-timeline: timeline;
      }

      @layer override {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 50px;
        }
      }

      @layer base {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 100px;
        }
      }
    `
  },

  {
    title: '@scroll-timeline override update with appended sheet 1',
    style: `
      @layer base, override;

      #target {
        animation-timeline: timeline;
      }

      @layer override {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 50px;
        }
      }
    `,
    append: `
      @layer base {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 100px;
        }
      }
    `
  },

  {
    title: '@scroll-timeline override update with appended sheet 2',
    style: `
      @layer base, override;

      #target {
        animation-timeline: timeline;
      }

      @layer base {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 100px;
        }
      }
    `,
    append: `
      @layer override {
        @scroll-timeline timeline {
          source: selector(#scroller);
          start: 0px;
          end: 50px;
        }
      }
    `
  },
];

for (let testCase of testCases) {
  promise_test(async function() {
    assert_true(
      CSS.supports('animation-timeline', 'foo'),
      'This test requires @scroll-timeline support');

    var documentStyle = document.createElement('style');
    documentStyle.appendChild(document.createTextNode(testCase['style']));
    document.head.appendChild(documentStyle);

    var appendedStyle;
    if (testCase['append']) {
      document.body.offsetLeft;  // Force style update
      appendedStyle = document.createElement('style');
      appendedStyle.appendChild(document.createTextNode(testCase['append']));
      document.head.appendChild(appendedStyle);
    }

    scroller.scrollTop = 25;
    await waitForNextFrame();
    assert_equals(getComputedStyle(target).width,
                  getComputedStyle(reference).width);

    if (appendedStyle)
      appendedStyle.remove();
    documentStyle.remove();
  }, testCase['title']);
}
</script>