Untitled

<!DOCTYPE html>
<html>
<head>
<style type="text/css">
select {
height: 42px;
}

.sel optgroup {
  font-weight: bold;
  color: red;
}

.sel option {
color: black;

}
</style>

</head>

<body>

<select class="sel">
  <optgroup class="group" label="Swedish Cars">
    <option value="volvo">Volvo</option>
    <option value="saab">Saab</option>
  </optgroup>
  <optgroup label="German Cars">
    <option value="mercedes">Mercedes</option>
    <option value="audi">Audi</option>
  </optgroup>
</select>

</body>
</html>