Fluid fixed block with left margin

[Seprex]

I need to put fixed block on the page. But it should be the fluid container's size (which have auto left-right margin) and left margin 160px inside container.HTML\[code\]<div id="container"> <div id="header">Some fixed panel</div> Some other scrollable markup</div>\[/code\]CSS \[code\]#container { width: 90%; max-width: 1280px; padding: 0px 20px 20px 20px; margin: 0 auto; min-width: 940px; position: relative; z-index: 1;} #header { width: 100%; height: 60px; position: fixed; margin-left: 160px; top: 0; z-index: 60; }\[/code\]And I can't make fixed panel to get correct width. Somehow this block get width not from container, but from window.Need some solution without JS.Tnx in advance.