Hello.
Yes, the countdown can be any size you wish, however, some of the styles (jedi, dath and carbointe) use images for the look, so you will have to also resize these as well. There are, however, pure CSS styles (TIE-fighter and c-3po) that can be resized only by changing the CSS.
Which style are you going for? Regardless, fret not! the answer will be provided!