This is the cool part you can make it what you want where you want.
This line has pretty much everything so use this one to add or subtract from the others to come up with what you want.
.customlink a:visited { color: #FFFFFF; text-decoration: none; font-weight:bold;font-size: 18px; }
Add this
text-decoration: none; to any of the link states that you don't want underlined.
Add this
font-weight:bold;font-size: 18px; to change font size.
Add this
color: #FFFFFF; to adjust the color.
This example should make the text go bold when you mouse over and the current page is now bold.
<style type="text/css">
<!--
.customlink a {color: #FFFFFF;text-decoration: none; font-size: 18px; }
.customlink a:visited { color: #FFFFFF; text-decoration: none; font-size: 18px; }
.customlink a:hover { color: #FFFFFF; font-weight:bold; font-size: 18px;}
.customlink a:active {color: #FFFFFF;text-decoration: none; font-size: 18px; }
.select a {color: #254117;text-decoration: none; font-weight:bold; font-size: 18px;}
-->
</style>