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chromium/third_party/blink/web_tests/external/wpt/css/css-backgrounds/animations/background-color-animation-will-change-contents-ref.html 

<!DOCTYPE html>
<style>
.box {
  width: 600px;
  height: 600px;
  background-color: rgba(0, 200, 0, 1);
}
</style>
<body>
  <div class='box'></div>
</body>