Forst to assist in matching the design,,,admin > config > layoutsettings > Categories-Tabs Menu ON/OFF > turn them to off or "0".
to ease this for you if can determine the height & width of your total head area in your design; make a jpg image 800x150px in size with your green bar placed at the bottom and Name it header_bg.jpg and place it in your template custom/images folder
I guessed at the 800x150 dimensions and this should match your design. You might then have to adjust the width of the mainWrapper in the css to match also.
then this in your css will get this image displayed.
You can of course make this a gif if you choose