that divider is actually part of an image. if you want it thinner, you can set the size to 1, or you can play with some CSS. a way i usually do it is like this:
between your <style> tags:
CODE
span.hr {
border-bottom:1px solid black; display:block; margin:10px 0; width:100%;
}
and where you want the divider to show up:
CODE
<span class="hr"></span>