<!DOCTYPE html>
<style>
#mask {
width: 200px;
height: 200px;
overflow: hidden;
border-radius: 10px;
border: 4px solid red;
background-color: blue;
position: relative;
display: inline-block;
}
.content {
width: 50px;
height: 50px;
}
.composited {
will-change: transform;
}
</style>
<p>Testing masks on compositing layers. Left and right columns should look the same.</p>
<div id="mask">
<div class="content" style="left: 175px;top: 175px;background: black;position: absolute;"></div>
</div>
<div id="mask" class="composited" style="left: 50px">
<div class="content" style="left: 175px;top: 175px;background: black;position: absolute;"></div>
</div>