<!DOCTYPE html>

<html>
<head>
  <style type="text/css" media="screen">
    body {
      margin: 0;
    }
    
    .box {
        height: 200px;
        width: 200px;
    }
  </style>
</head>
<body>

    <div class="box" style="background-color: red;"></div>
    <div class="box" style="background-color: green;"></div>

</body>
</html>