Why isn't this design center aligning?

http://jsfiddle.net/C2LAV/

I'm attempting to make the design fill the whole screen unless it exceeds 30% of the total screen width. Then, if it exceeds the 30%, it should center align. W开发者_StackOverflowhy isn't it doing so?

updated version, still not working: http://jsfiddle.net/C2LAV/5/

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You're trying to use headerObj, which isn't defined, you need something like:

var headerObj = document.getElementById("header");

You can test it out here. For the other piece, the actual centering, you just need to set the margin, like this:

contentObj.style.margin = "0 auto";

You can test that out here.