What's the trick for fixed positioned elements inside a liquid layout?

开发者_如何学Python

So I have a fixed positioned element that resides in an expanding element.

What's the trick to keep it in the same place whether the browser is at 1024px wide or 2000px ?

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The fixed-size element must be display:block, and have a margin:0 auto. To have fixed position, position has to be set via javascript, and updated when the window is resized.