EXAMPLE
Run 
<!DOCTYPE html>
<html>

<head>
	<title>The grid-auto-columns property in CSS</title>
	<style type="text/css">
		#grid {
		  height: 100px;
		  display: grid;
		  grid-template-areas: "a a";
		  gap: 10px;
		grid-auto-columns: minmax(max-content, 2fr);
		}
		
		#grid > div {
		  background-color: blue;
		}
	</style>
</head>

<body>
	<div id="grid">
		<div id="item1"></div>
		<div id="item2"></div>
		<div id="item3"></div>
	</div>
</body>

</html>