HTML layout trouble

Question

Can anyone please help?

I am trying to do the following layout in HTML and CSS. This image is just a rough representation of the general layout for a website. The top bar (or header) will be e.g. light grey and the sidebar 1 will be the same colour. The sidebar 1 also has a rounded bottom left corner and the sidebar 2 has a rounded top right hand corner. The effect I’m trying to recreate is that the header will “flow” into the sidebar 1 and that the sidebar 2 will “flow” into the footer. So far I have the boxes coded so that it seems that they are touching and I also have the rounded corners done. But what Ive been stuck with for the whole day now is how to do the colours so that it seems that the 1 is flowing into the next one. Here is an example of what I have so far (still very rough as I am just trying to block out the shapes etc.) hansmoolman.com

The relevant section in the website above is the one called "This is the main container" which is about half way down the page and contains the sidebar 1 (the one with the Twitter feed) and sidebar 2 (the one with all the Lorenm Ipsum stuff). The top bar will be the one with the logo and navigation stuff. The footer is not yet implemented.

Can anyone suggest how I can do this? I am trying to stay away from a background image that will represent this as the sidebar 1 and 2 should be able to grow dynamically and independently of one another should more content be added. Or can this done with a background image/images?

Can anyone please help as all the solutions I have been working on has become very messy with boxes inside and on top of other boxes. It does not look good code wise and I am concerned that it might not display as intended on all devices.

If more clarity or code is needed on this question just let me know and I can provide both.

Thanks in advance

*Edit - this is a possible solution as suggested by flem

Answer 1

Build your layot with divs like this (spacing just for visibility):

You will also need an element behind each of the rounded corners with the opposite colour. (You only need to do one of them if you set your body background colour.)