Converting Site header from fixed to floating

Hi, Can you advise if the header/masthead in Fabulous Fluid can be changed to a fixed position so that the page content flows under the site navigation as the viewer scrolls down? This similar to the Parallax and Clean Business themes. I would like to stay with the FFluid theme as it best suits the client. I tried this: #masthead {position: fixed;} but it did not work fully. Terrific new themes by the way. I am investigating updating a client from Catch Box Pro to Fabulous Fluid. Thanks in advance, J Macwebster