pt; min-height: 40pt; }

.mask { position:fixed; left:20px; right:0; top:0; bottom:0; background: black; }
  </style>
</head>
<body>

<!-- mask off differences on the right side -->
<div class="mask"></div>

<select><optgroup label="label"><option>option</option></select><br>
<select class="big"><optgroup label="label"><option>option</option></select><br>
<select class="lh"><optgroup label="label"><option>option</option></select><br>

</body>
</html>
