<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>calc()</title>
  <link rel="stylesheet" href="style.css" />
</head>
<body>
  <header class="page-header">
    <h1>calc()</h1>
    <p class="lead">Do math in CSS across different units.</p>
  </header>
  <main class="demo">
    <div class="calc">Width = 100% - 4rem</div>
  </main>
</body>
</html>