What a Checkbox looks like depends on what browser you are viewing it with,
not the code. I haven't looked at it yet, but there is probably a way to
make it look the way you want by using CSS, although this would, of course,
require that the browser support whatever CSS properties you use to obtain
that look. In my opinion, however, changing the look of elements such as
checkboxes is not usually a good idea, and is more effort than it is worth.
I feel this way because when the look of common elements such as checkboxes
look too different some people hesitate to use them because they think they
are part of a Java Applet, or they may not recognize them quite as quickly.
Also, for the few people that still use browsers that don't support CSS,
they will still see the plain checkbox anyway. So unless the look of
standard controls like this is EXTREMELY important to your page, don't
bother trying to change how they look, because most people won't care anyway
(other elements might be worth the effort, but not little things like
checkboxes and radio buttons).
