Hi Billy...
Soooo... This is actually a support forum for the themes we sell. In the spirit of openness and sharing and community goodwill however, here goes:
1. The big browsers, Internet Explorer, Chrome, Firefox, Safari and Opera, all use different rendering engines. Even different versions, of the same browser, notably IE, will render differently in many cases. This has led to a whole sub-discipline of web development, which deals exclusively with ensuring cross-browser compatibility. It's mostly done by conditional CSS, something like this:
If Internet Explorer 6, then use this CSS. If FireFox then use this CSS.
Teaching this skill to someone is beyond the scope of this forum, and this answer. The web however, is a rich resource of knowledge on the subject, and learning to use Google (http://www.google.com) to surface that information is a great skill to acquire.
2. Yes, certainly. In fact, we have a blog-post, specifically about that. You DO read our blog, right? :) http://goo.gl/KYh0M
3. Glad to help. Get your Google on, you won't be sorry...
Cheers.