In side a wrap div of width 800px, I have a sidebar div with the following code: float:left; width:50%; background-color:white; font-size:1em; position:fixed; The sidebar won't take up 50% of the wrap (400px) but 50% of the browser window (1350px). *Why?* The div called main sits next to the sidebar on the right with width 50% and it is around 400 px.