The Juice Box Bandit's blog: "Your Profile Breakdown"

Now we're getting somewhere where we can customize!

This section of coding is your "Header Pic" or "Welcome Mat" to your profile.

It is located below your User Interaction Links, Name, and CustomURL section.

This is where you find, make, or adjust a picture to set the theme to your profile.

I've used a border to outline this section in red.

The CSS will be posted after this picture:

#userpagecontentstyle .userprofile_headerbar {
   height: ;
   background-color: transparent!important;
   background-image: url();
   background-repeat: ;
   background-position: ;
   border: ;
   -moz-border-radius: ;
}

Portions in red are optional, most people tend to exclude them.

The height should be about the same as the picture you chose to be your welcome mat.

For the example picture I used a "1em red ridge" border to outline the section in red.

You don't have to have one, I usually don't as the borders on the rest the profile tend to be enough.

The background-color I typically leave transparent out of habit, as having one set can override the picture at times.

As for your background-image, put the URL (http address) to your picture in the parenthesis: (←these things→).

If your image isn't meant to be tiled (or looks like crap tiled)

I'd recommend background-repeat be set to: no-repeat.

Is your picture huge and you just want a section of it to show?

Maybe you just want it to be anchored in a certain way?

background-position you can use terms like: Top, Center, Bottom; with Left, Center, Right.

For more info on background positioning and css I recommend checking out w3schools via quick google search.

If you have questions feel free to ask.