Is there any documentation available for creating new themes? I see nothing related to themes under the "documentation" link, and Google isn't much more helpful. We've got yaf.net integrated into our .net application, but right now it sticks out like a sore thumb. At a minimum we need to be able to insert our own header and footer, and change the colors and typography. This doesn't seem as though it would be rocket science, but I really hate to start hacking at files without first reviewing some documentation as to what does what.
YAF's themes are seperated into a subfolder under the "~/themes" folder inside YAF. They are mainly CSS driven - so a copy of firebug and a little time and you can modify the appearance quite easily. Recommeded copy theme folder to new name folder, and copy theme XML file in ~/themes folder to a new name. Edit theme's XML file to reflect new folder name for that theme. Then you can choose that theme in YAF and begin modifying, and if make mistake, can choose back to another theme so forum stays online, etc. Can also enable personal themes, create a dummy user, and set the 'new theme' to that dummy user's account so you can develop without disturbing rest of users.
Not much documentation on theme editing - but they are pretty straight forward if you have CSS experience.
To add content to pages, such as all pages, I used modifications to default.aspx - that will affect ALL pages in YAF. It is essentially the 'template' file for the site -- and YAF runs as a .NET control in that page. If you need to change individual pages, there is way to do it using the theme folder. Check out the XML for the YAFMobile theme and the ./Mobilepages folder - theme's XML file supports overriding pages individually - might be useful for working with pages and not 'overwriting' core code -- then when new version upgrade, you can just update your theme files and not have to worry about changing core code.