in-width: 20px;
  min-height: 20px;
  width: 100%;
  height: 100%;
  content: '';
  display: block;
}

.ar {
  aspect-ratio: 1/1;
  min-width: 20px;
  min-height: 20px;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/check-layout-th.js"></script>

<body onload="checkLayout('.item')">

<body>

<div class="container">
  <div class="item" style="justify-self: start; align-self: start;" data-expected-width="20" data-exp