Well done! Looks fine to me. Check it in as many browsers as you can. Also a handy tip is 'browsershots' which you can find with a quick search online.

Yes, the other search box will probably need the same treatment. First add an ID to it. Then style that ID.

It is a good technique for a lot of Zen Cart. Mostly Zen has the IDs and classes that you need to style everything (it is a good e-commerce solution) but occasionally you come across extra things that you would like. In that case just put them in yourself!

Glad you had one of those happy moments that make up for all the frustration!