Problem to control div with blueprint css

I´m having a problem with divs when I´m trying to apply background-color to #header for example so it will cover all of the header. it dosen't show any changes that I made to the css of the #header, #maincontainer and more can you please help me I have tried so many things and nothings seems to work.

Here is the Html sample :

<div id="wrapper">
   <div class="container">
   <div class="span-24 showgrid">
   <div id="header">
   <div id="logo"><img src="logo.png" alt="Iris logo"></div>
   <div id="slogan">
   <h1>Íris</h1>
   <h2>Ættleiði开发者_运维技巧ngartengd fræðsla</h2>
   </div>
   <div id="searchbar"><input class="text" onfocus="this.value=&#39;&#39;" type="text"     name="searchbar" value="Leita.."></div>
    </div><!-- end .header -->

Here is the rest of the HTML if you prefer to see to all : http://pastebin.com/8AyENrdn

It's hard to tell from what you have described and no CSS - Try this

#header {overflow:hidden;background:#eee;}