<!DOCTYPE html>
<html>
  <head>
    <title>:first-child test</title>
    <style type="text/css">
      html             { background: yellow;}

      p { width: 20px; height: 20px; background: orange; float: left; margin-left: 10px; }
      div { clear: both; }
      #p1 { background: green; }
      #p2 { background: green; }
      #p3 { background: green; }
      #p4 { background: green; }
   </style>
  </head>
  <body>
    <div id="d1"><p id="p1"> </p><p> </p></div>
    <div id="d2"> <p id="p2"> </p><p> <