Specifying a non-static position, e.g., position: absolute/relative
on a node means that it will be used as the reference for absolutely positioned elements within it http://jsfiddle.net/E5eEk/1/
See https://developer.mozilla.org/en-US/docs/Learn/CSS/CSS_layout/Positioning#Positioning_contexts
We can change the positioning context — which element the absolutely positioned element is positioned relative to. This is done by setting positioning on one of the element's ancestors.
#outer {_x000D_
min-width: 2000px; _x000D_
min-height: 1000px; _x000D_
background: #3e3e3e; _x000D_
position:relative_x000D_
}_x000D_
_x000D_
#inner {_x000D_
left: 1%; _x000D_
top: 45px; _x000D_
width: 50%; _x000D_
height: auto; _x000D_
position: absolute; _x000D_
z-index: 1;_x000D_
}_x000D_
_x000D_
#inner-inner {_x000D_
background: #efffef;_x000D_
position: absolute; _x000D_
height: 400px; _x000D_
right: 0px; _x000D_
left: 0px;_x000D_
}
_x000D_
<div id="outer">_x000D_
<div id="inner">_x000D_
<div id="inner-inner"></div>_x000D_
</div>_x000D_
</div>
_x000D_