<select class="bigselect">
<optgroup class="bigelements">

<option>乙</option>
<option>丙</option>
<option class="afire">丁</option>
<option>戊</option>
<option>己</option>
<option>庚</option>
<option>辛</option>
<option>壬</option>
<option>癸</option>
</optgroup>
</select>

.bigselect {
    font-size: 48px;
    width: 85px;
    height: 90px;
    max-width: 85px;
}

.bigelements {
    font-size: 1em;
    width: 85px;
}

.afire
{
    color: red;
}