I'd like to change the appearance of things like "basic user info" "human avatar" "wish list" the comment box, etc. Can anyone tell me how to do this?

This is a pretty vague question so can you specify exactly what you want to do?

Well I've already figured it out a bit. I've managed to change the background color of the boxes to black, though trying to use an image didn't seem to work. I can't seem to change the color of the "header" of the boxes, only make it invisible. I also sort of was able to change the text, but I can't figure out how to make the header text a different color than the rest of the text. aka the words like, "Basic Userinfo" and "Wishlist". Or really change any of it's properties because I would also like to center it as well.

To change your header, you would use ".header" and edit it like anything else. So ".header {background-color:COLOR; color:TEXTCOLOR; text-align:center;}" etc.

You have this in your code currently ".info_block, , , , .header, .forminput {background: rgba(0, 0, 0, 1); border: none; background: transparent;}"

So remove the bolded part, so you can edit the header stuff properly. :3

May I ask what code you were using to try and make the backgrounds an image rather than a solid color?