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<!DOCTYPE html>
<title>Layout Instability: no layout shift if transform change counters location change</title>
<link rel="help" href="https://wicg.github.io/layout-instability/" />
<style>
body { margin: 0; }
#transformed { position: relative; transform: translateX(20px); width: 100px; height: 100px; background: blue; }
#child { width: 400px; height: 400px; }
</style>
<div id="transformed">
<div id="child"></div>
</div>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/util.js"></script>
<script>
promise_test(async () => {
const watcher = new ScoreWatcher;
// Wait for the initial render to complete.
await waitForAnimationFrames(2);
// Modify the transform and the location at the same time, and the values
// cancel each other visually, for which no shift should be reported.
transformed.style.transform = 'translateY(100px)';
transformed.style.top = '-100px';
transformed.style.left = '20px';
// Change size of child, for which no shift should be reported, either.
child.style.width = '300px';
await waitForAnimationFrames(2);
// No shift should be reported.
assert_equals(watcher.score, 0);
}, 'no layout shift if transform change counters location change');
</script>
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