Here is a website theme for all your Harry Potter needs! This, obviously, is the Gryffindor theme. The other houses are here, also, as well as a Dark Mark background and graphic. Please refer to the rules when using this or any other website theme from this site.
And a special disclaimer for this theme: I claim no ownership of the copyrights, nor am I making any money from this theme. It was done for entertainment as a fan tribute.
Above are only two examples of this theme - all files can be found here: Files.
