The issue at hand arises from the fixed sizes of the elements in the source code, a consequence of how the code was initially written. Rather than extensively altering the source code to accommodate multiple styles, it would be more effective to simply utilize CSS along with some additional HTML.
If your HTML were structured as follows:
<label for="first">Custom styled select box</label>
<div class="styled-select">
<select name="first">
<option>First option here</option>
<option>Second option</option>
</select>
</div>
<label for="second">Custom styled select box, featuring enlarged text</label>
<div class="styled-select">
<select name="second" class="enlarged">
<option>Initial option</option>
<option>Secondary option</option>
</select>
</div>
Your stylesheet might resemble the following:
.styled-select {
width: 240px;
height: 34px;
overflow: hidden;
background: url(http://cdn.bavotasan.com/wp-content/uploads/2011/05/down_arrow_select.jpg) no-repeat right #DDD;
}
.styled-select select {
background: transparent;
width: 268px;
padding: 5px;
border: 1px solid #CCC;
font-size: 16px;
height: 34px;
-webkit-appearance: none;
-webkit-border-radius: 3px;
border-radius: 3px;
}
select.enlarged {
font-size: 24px;
padding-top: 1px;
padding-right: 55px;
padding-bottom: 0;
}
View this implementation utilizing this jsfiddle.
(Source: bavotsan.com)