chromium/third_party/blink/web_tests/fast/layers/self-painting-outline.html

<style>
    div { padding: 50px; }
    div div {
        padding: 0;
        width: 25px;
        height: 25px;
        background-color: rgb(127, 127, 127);
        outline: 40px solid rgba(0, 0, 0, 0.5);
     }
</style>
<div>
    <div></div>
</div>
<div>
    <div style="overflow: hidden;"></div>
</div>