<html>
<head>
  <style>
    div    { width:  100px; }
    div.a  { height:  30px; background: lightblue;  }
    div.b  { height: 100px; background: lightgreen; }
    div.c  { height:  10px; background: black;      }
  </style>
</head>
<body>
  <div class="a"></div>
  <div class="b"></div>
  <div class="c"></div>
</body>
</html>