calc() CSS Function - Playground Example

<!DOCTYPE html>
<html>
<head>
<style type="text/css">
.boxcalc {
  width: calc(100% - 100px);
  border: 2px solid red;
  background-color: #ccc;
  padding: 10px;
  text-align: center;
}
</style>
</head>
<body>
<div class="boxcalc">Example using the calc() CSS function.</div>
</body>
</html>