To add to what GR has mentioned, creating GUI elements requires a bit of imagination and creativity.
Think of the controls as lines, rects and filled rects and then combine them to produce buttons, scrollbars, progress bars, etc. For example, a simple text box will just need one filled rect (with white) and a rectangular border around it w/ a diff color. To enhance it, you can use lines for the border instead and color the top and left line w/ a darker color and the right and bottom line w/ a lighter shade. This will produce depth. This can go on and on w/ the other GUI controls.
