<!DOCTYPE HTML>
<!--
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<html><head>
  <meta charset="utf-8">
  <title>Reference: nested orthogonal writing-mode subgrids with percentage column-gap</title>
  <link rel="author" title="Mats Palmgren" href="mailto:mats@mozilla.com">
  <link rel="stylesheet" type="text/css" href="/fonts/ahem.css">
  <style>
html,body {
  color:black; background-color:white; font:24px/1 Ahem; padding:0; margin:0;
}

.grid {
  display:inline-grid;
  grid:100px 375px/300px;
  border:3px solid;
  width: 300px;
  height: 500px;
  background:lightgrey;
  row-gap: 25px;
}
span {
  grid-row:2;
  background:cyan;
  width:50px;
}
</style>
</head>
<body>

<div class="grid">
  <span>ccc</span>
</div>

</body>
</html>