I have my main page, called layout.html. I want a drop down menu that I have completely coded on ddm.html to appear in layout.html.

I know I can do this with PHP, but i'd rather develop it offline, CSS should be able to do this, I just dont know the code.

I do know the code to fetch pages with CSS Vars, but that hasnt worked for a html page with content.

CSS can't do what you want. CSS was created for presentation. You can style HTML with it, but it wasn't made to include one html file into another. The way to do what you want is with PHP or another scripting language. It's pretty trivial to do though and if you install a server and scripting language on your computer you can still develop your sites offline.

Installing Apache and PHP on your local machine probably won't be the easiest thing you'll ever do, but it also won't be the hardest.

Do you have a Windows-based (2000 or XP) PC? If so, you can configure it as a web server and potentially install PHP that way.

It'll save you a buttload of time in development if you can get your server configged properly.

You do realize PHP arguably works better on Linux.. SO you could use Linux instead of just Windows. Anyways more than PHP can do it and CSS stands for Cascading STYLING Sheet. Notice there's nothing saying processor? It doesn't process anything (well besides the actual styling but does it really even count..) so it's impossible. You do realize you could do it without any server side language though. There's options. I don't have enough time to explain further (have to finish a few freelancing jobs, get my own new site running, and install iMap :S) but they're out there.. Google it.