How to change width to fill the remaining space (CSS)

Question

Take a look :

Result should be

Answer 1

#sidebar { float:left; width:280px; }
#content { margin: 0 0 0 280px; } /* dont float it */

http://jsfiddle.net/auTbG/1/

You will have problems if you have floats inside of #content and you try to clear them, though.