replace <?php wp_list_categories('title_li=&show_count=1'); ?>
with this:
<?php
$variable = wp_list_categories('echo=0&show_count=1&title_li=');
$variable = str_replace(array('(',')'), array('(<span class="cat-count">','</span>)'), $variable);
echo $variable;
?>
and put this in your stylesheet
.cat-count{
font-size: 12px;
}
And change the font-size to your liking.
Oops that only changes the font size of the numbers. to change the whole “(5)” use this:
<?php
$variable = wp_list_categories('echo=0&show_count=1&title_li=<h2>Categories</h2>');
$variable = str_replace(array('(',')'), array('<span class="cat-count">(',')</span>'), $variable);
echo $variable;
?>