<!DOCTYPE html>
<html>
  <head>
    <style>
       html {
        background: #FFFF00
       }
       body {
        margin: 0px;
        background: #FF00FF
       }
       div {
        width: 1280px;
        height: 720px;
       }
    </style>
  </head>
  <body>
      My background is purple, but the rest is yellow
  </body>
</html>