[css] Set size on background image with CSS?

Not possible. The background will always be as large as it can be, but you can stop it from repeating itself with background-repeat.

background-repeat: no-repeat;

Secondly, the background does not go into margin-area of a box, so if you want to have the background only be on the actual contents of a box, you can use margin instead of padding.

Thirdly, you can control where the background image starts. By default it's the top left corner of a box, but you can control that with background-position, like this:

background-position: center top;

or perhaps

background-position: 20px -14px;

Negative positioning is used a lot with CSS sprites.