Percentage width for fixed elements?

Question

I have html like this:

    
...
    
...


#con         


        

Answer 1

The first div's 70% refers to 70% of the width of #content.

The second div's 70% refers to 70% of the width of the viewport.

If you add this CSS, the two div's are the same width:

html, body {
    margin:0; padding:0
}

Live Demo