[SOLVED] Giving widget a background

On my website I have a new widget area in the header. In this area I've put a custom menu (shows a certain menu, depending on which page you are).
I've given the custom menu a class for the ul element which forms the menu, and I'm able to style this with css-inserts - works like a charm!
The ul is wrapped in a div, and I've given this div an ID. I'm trying to style this container with css-inserts, but it doesn't work! What am I doing wrong!?

I'm using WordPress 3.4.1 + Atahualpa 3.7.7

This is the generated code:

<div id="sub-menu-top" class="bfa_widget_area">
<div id="advanced_menu-2" class="widget widget_advanced_menu">
<div id="bam" class="menu-actueel-container">
<ul id="menu-actueel" class="offermenu">
<li id="menu-item-40" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-40"><a href="http://localhost/?page_id=7">agenda</a></li>
<li id="menu-item-43" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-43"><a href="http://localhost/?page_id=9">nieuws</a></li>
<li id="menu-item-42" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-42"><a href="http://localhost/?page_id=11">in voorbereiding</a></li>
<li id="menu-item-41" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-41"><a href="http://localhost/?page_id=15">contact</a></li>
</ul>
</div>
</div>
</div>