Percentage width for fixed elements?

Question

I have html like this:

    
...
    
...


#con         


        

Answer 1

This weird behavior (great question!!) can be referred about the fact that the relative div (first) take the width looking at his father. The second one just look at the viewport, no matter who is its father (and what width is set to its father)!

This can fix your problem:

body,html{
    padding:0;
}

Edit -> Fiddle