<!DOCTYPE html>
<html>
<head>
  <style>
    div {
      background-color: yellow;
      height: 30px;
    }
    .container {
      width: 100px;
    }
    .stretch {
      width: 40px;
      background-color: white;
      display: inline-block;
    }
    .left-spacer {
      width: 30px;
      float: left;
    }
    .right-spacer {
      width: 30px;
      float: right;
    }
    body {
      background-color: black;
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="left-spacer"></div>
    <div class="stretch"></div>
    <div class="right-spacer"></div>
  </div>
</body>
</html>
