<!DOCTYPE html>
<html>
<head>
<style type="text/css">
select {
    width: 100px;
    height:100px;
    font-family: sans-serif;
    font-size: 12px;
    border: 1px solid black;
    box-sizing: border-box;
}
#cover {
    position: absolute;
    width: 100px;
    height:300px;
    background-color: black;
    left: 80px;
    top: 0px;
}
.red { color: red; }
</style>
</head>
<body>
<select size="4">
    <option>One</option>
    <option class=red>Two</option>
</select><br><select size="4">
    <optgroup label="Optgroup1"></optgroup>
    <optgroup label="Optgroup2" class=red></optgroup>
</select>
<div id=cover></div>
</body>
</html>