Push Elements Left or Right with the float Property

Summary

Floating elements are pushed to either the left or right of their containing parent element.
Floating elements are removed from the normal flow of a document.

Final Code

<head>
  <style>
    #left {
      float: left;
      width: 50%;
    }
    #right {
      float: right;
      width: 40%;
    }
    aside, section {
      padding: 2px;
      background-color: #ccc;
    }
  </style>
</head>
<body>
  <header>
    <h1>Welcome!</h1>
  </header>
  <section id="left">
    <h2>Content</h2>
    <p>Good stuff</p>
  </section>
  <aside id="right">
    <h2>Sidebar</h2>
    <p>Links</p>
  </aside>
</body>