I created a new blog recently: sacredpixels.com
I’m using the sapphire theme what I really like, the only thing though is that I’d like the whole blog (including header) to be about 30% wider… I’m pretty sure this is possible with the custom CSS option. Only thing is that I don’t know how to do it.. Is there anyone who can help me out?
The CSS upgrade is not recommended for people with no CSS experience. There’s no official support for it, and only a couple of forum volunteers who know what they’re doing with it. You’re pretty much on your own. Have you read the resources recommended in the CSS forum?
Widening a theme with CSS is possible but it’s actually non-trivial. The aesthetic of most themes are closely tied to fixed size backgrounds and art assets, so–in many cases–those would need to be enlarged proportionally or edited as well.
As raincoaster mentioned, I would recommend reading up thoroughly. This article is a good start as well as the tutorials it links to: