CSS problem in Matrix

Hi:
I am trying to mdify the sidebar.tpl in Matrix to add some links.
However I am having a problem with the css for that part.
My class properties seems to get overridden by the parent class properties for the sidebar page.

I have tried it several ways but can't get it to work.

The last (unsuccessfull way was this:
<-- On sidebar.tpl page ---- -->

<table width="90"
border="0"
cellspacing="0">
<tr><td>
<a href="../index.html" class="mainlevel">Home</a></td></tr>
<tr><td><a href="../about.html" class="mainlevel">About</a></td></tr>
<tr><td><a href="../contact.html" class="mainlevel">Contact</a>
</td></tr>
</table>
<p>&nbsp;</p>
<div id="gsSidebar" class="gcBorder1">
{* Show the sidebar blocks chosen for this theme *}
{foreach from=$theme.params.sidebarBlocks item=block}
{g->block type=$block.0 params=$block.1 class="gbBlock"}
{/foreach}
{g->block type="core.NavigationLinks" class="gbBlock"}
</div>

<-- ----- End sidebar.tpl page ----- -->

<-- ---- In theme.css page ---- -->

#gsSidebar a.mainlevel:link, a.mainlevel:visited {
background-color: #B9D4FF;
border-bottom: 1px solid #FFFFFF;
font-size: 12px;
font-weight: bold;
color: #333333;
text-align: left;
padding-left: 10px;
text-decoration: none;
display:block;
}
#gsSidebar a.mainlevel:hover {
background-color: #003399;
color: #FFFFFF;
text-decoration: underline;

<-- ------- End theme.css page part ------ -->

Thanks for your help.
I just can't seem to get these css properties to work instead of the
"global" ones for the page.