selector { width: 150px; height: 65px; }

Height and Width in Pixels.

Width is how many pixels the image runs along the x-axis.

Height is how many pixels the image runs along the y-axis.

If this image does not conjure sweet memories of PhotoShop or a hundred other programs, it may be time you enroll in a remedial graphics class.

Or perhaps you don't need a high-stepping image background after all. If you do... and yet this feels quite mystifying... try a search on Altavista, eh?