I've started this process by adjusting the base theme. Now I'm trying to clean up theme elements in CSS to fit a light theme rather than dark. If you notice a particular area that looks like it hasn't been updated, let me know.
I'm currently working on tables, TM boxes, and the twitter feed, so you don't need to tell me about those. Done! The Twitter Widget on the main page hasn't updated for me yet, but it looks right on Online Help Landing Page, so I trust it'll get there soon.