Thanks but I suppose that did vot resolve the problem.

I removed all the red code mentioned but I did not understand the last info:
But then it still looks like there are two sidebars, for all 3 sections (content + leftsidebar + rightsidebar) are painted on the 3 background images:
What does this mean?
One more thing:
How do I increase the width of the content column ( first column) ?