<!DOCTYPE HTML>
<html>
  <head>
    <meta http-equiv="Content-type" content="text/html; charset=utf-8">
    <style type="text/css" media="screen">
      
      div {
        -webkit-box-sizing: border-box;
      }
      .solid {
        position: absolute;
        width: 100px;
        height: 100px;
        background-color: green;
      }

      .opacity { opacity: .5; }
      .a { top: 0px; left: 0px;}
      .b { top: 200px; left: 200px;}
      .c { top: 200px; left: 0px;}
      .d { top: 0px; left: 200px;}
      * { margin: 0; padding: 0; }
      .composited {
        -webkit-transform: translateZ(0);
      }

    </style>
  </head>
    <div class="opacity">
      <div class="solid a">1</div>
      <div class="solid b">2</div>
      <div class="solid c">3</div>
      <div class="solid d"></div>
    </div>

</html>