I have this:

.container{
	width: 96%;
	/*min-width: 866px;*/
	background-color: #F30;
	padding: .5em;
	/*background: url(images/bgmain.png) repeat-y;*/
	color: #333;
	}
#top{
	color: #000000;
	background-color: #6A5D5C;
	}
#topmenu {
	background-color: #6A5D5C;
	}
#topundermenu{
	width: 100%;
	background-color: #9F9F9F;
	text-align: center;
}

and in page:

<div id="container" class="container">
	<div id="top">
...
	</div>
	<div id="topmenu">
...
	</div>
	<div id="topundermenu">
...
	</div>
</div>

the problem is that topundermenu is smaller than top and topmenu