In need of some LJ tech help...

[seticat]

Okay folks out there who know how to do this LJ stuff better than I, *IF* I should get off my tush and come up with the code somewhere [either html or css], how do I upload/modify theme code to LJ? Right now all I want to do is add a banner at the top of the page and change the heading font style and size, but I absolutely suck at css and the FAQ on LJ isn't coming across very clear to me.

Help?