<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <title>background on body should fill the viewport</title>
  <style>
   html { background-color:transparent; background-image:none; }
   body { background-color:yellow; margin:8px; color:navy; }
  </style>
 </head>
 <body>
  <p>The entire viewport should be yellow.</p>
 </body>
</html>