forcing a div to the left - css

Question

How can I get <div id="green_bar"> to overlap <div id="top_header"> and stop at the left edge of the logo? I'm trying to get the green bar to expand to the left when the screen width is expanded, but I want it to stop at the left edge of the logo.
I've tried position: absolute; on #green_bar but it expands it 100% across the screen.
JSFiddle: http://jsfiddle.net/hfgQt/14/
HTML:
<div id="header_bar"></div><!-- Grey line on top -->
<div id="top_header"><!-- begin top header -->
<div id="green_bar"></div>
<div class="wrap">
<div id="logo">
<a><h1>info</h1></a>
</div>
</div>
</div><!-- end top header -->​
CSS
.wrap {
margin:0px auto;
width:960px;
}
#header_bar {
background-color: #424243;
height: 25px;
}
#top_header {
padding:0px 0px;
background-color:#24303d;
background-image:url("http://i.imgur.com/kGjGG.png");
border-bottom:1px solid rgba(0,0,0,.4);
overflow:hidden;
}
#green_bar {
display: block;
height: 10px;
width: 100%;
background-color: green;
}
#logo {
float:left;
clear:both;
}
#logo h1 {
margin:0px;
padding:0px;
background:url(../images/logo.png) no-repeat;
text-indent:-9999px;
width:258px;
height:56px;
}
​

Answer 1

Try the snippet below.
As I understand your problem, the trick is to get something that is half of (browser width - 960px). That's the amount of the left margin. I used an extra wrapper div to cut out the fixed width (should be 960px, but I changed it to 480px to get it to look OK in jsfiddle). It's position: absolute to get it out of the flow. Then the inner div (#green_bar) simply has width: 50% to cut it down to half the width of both margins put together - the width of the left margin only.
It's hard to understand what you want, so I might have done the wrong thing. Let me know if you need any more help.
header {
padding-bottom:5px;
margin-bottom:35px;
background:#ffdf85;
border-bottom:1px solid #d4d4d4;
background-color:#ffdf85;
}
.wrap {
margin:0px auto;
width:480px;
background: rgba(128, 128, 0, .5);
overflow: hidden;
}
#header_bar {
background-color: #424243;
height: 25px;
}
#top_header {
padding:0px 0px;
background-color:#24303d;
background-image:url("http://i.imgur.com/kGjGG.png") no-repeat;
border-bottom:1px solid rgba(0,0,0,.4);
overflow:hidden;
position: relative;
}
#green_bar_wrapper {
position: absolute;
padding-right: 480px;
left: 0;
right: 0;
top: 0;
}
#green_bar {
width: 50%;
height: 10px;
background-color: green;
}
/* 3.0.0 Logo
----------------------------------------*/
#logo {
float:left;
clear:both;
}
#logo h1 {
margin:0px;
padding:0px;
background:url(http://i.imgur.com/kGjGG.png) no-repeat;
width:258px;
height:56px;
}
#logo h1 span {
text-indent: -9999px;
}
<header><!-- BEGIN HEADER -->
<div id="header_bar"></div><!-- Grey line on top -->
<div id="top_header"><!-- begin top header -->
<div id="green_bar_wrapper"><div id="green_bar"></div></div>
<div class="wrap">
<div id="logo">
<h1><a><span>info</span></a></h1>
</div>
</div>
</div><!-- end top header -->
</header><!-- END HEADER -->