Hello guys,
I'm trying to create a fluid background both horizontally and vertically.
I mean when the browser is stretched the background should adapt to the new size letting the same space around it.

Making it works horizontally is quite simply using 3 columns and setting margins and floats.
But how about vertically? The first idea I had is using 9 divs (3 inside each column) but how can I make the middle one growing and shrinking according to the browser side?

Let us say I want to have 20px margin both above and below so when the browser window is height 700px the div must be 660px, however when the browser window is shrunk to 500px the div must be 460px.

Thanks and have a nice day!