The white look is rather boring, and I'd like to change it with CSS if possible. How can I do this?

Check out the Profiles & Graphics Discussion forum. There are a lot of useful threads there, and if you get stuck on anything related to profiles you can ask there.

Here is a good place to start: Useful Profiles and Graphics Threads

Thank you very much :)

edit: I took a look but I still don't know where to input my CSS code

You can put your CSS within a blank section or within the "profile" section, both of which can be added to your profile via to the toolbox on the edit profile page!

I changed mine in Personal > Customize Sidebar > Profile and then pasted it in the given text box. Or you can click here, it should take you to the page I am talking about.

SubetaLodge has some CSS profiles if you're interested in an already-made one. That's what I used. Up until a few days ago I didn't know how to change it beyond the few options provided by subeta.

Where would I find the ones that are pre-made? I used to have a code for one that was made specific for me, but I lost it.

There are a few here on SubetaLodge: http://www.subetalodge.org/graphics

You can browse there, or you can either commission one from the profile forum or sometimes people post freebies, though you can't edit it without permission from the artist.

Hmm...it's only changing my profile over there, it's doing nothing on my profile in the subeta site directly... :/

edit: Hmm, it's getting really late. I might try and fix it tomorrow.

It should be submitted into the box in the link I gave you before, not the customCSS tab. That's the only thing I can see would get in the way. It's confusing, but the customCSS tab is for your view not your profile, so maybe that's why it's not working?

Yeah, it's a little confusing for me, lols.

edit: i just used a free one on tumblr for now