That is just the code of the semi-dynamic width. It is already included in the overall_header.html, so you don't have to add it.
If you resize your browser and hit refresh button, you will probably see a resized forum.
Example:
Your screen resolution is 1280x1024.
Your browser is maximized to the full screen resolution. If you now resize your browser, and it does not fit into the browser window anymore, just hit refresh and it will resize your forum.







