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chromium/third_party/blink/web_tests/external/wpt/css/filter-effects/reference/effect-reference-source-alpha-002-ref.html 

<!DOCTYPE html>
<style>
.rect {
    background-color: black;
    width: 100px;
    height: 100px;
    will-change: transform;
}
</style>
<div class="rect"></div>