APEX

I am new to CSS concept and Javascript.

I am having following query.

1. I have to set my application standard in terms of font size, color, etc...
what is the best way to do that..should I create a CSS file and put all my styles there and then use them in all the
Pages through the entire application.

2. Is by default we have one CSS file for each theme, i.e Is CSS file is Theme specific or Application Specific, If I will
create my own css file will it ovveride the default one. [can we have more that one css file in a application]

3. How can I see the default APEX CSS file.

4. As for javascript, where should I define the javascript functions, if I have to use that func in most of the pages through out the application.

Can anyone also proved me the link/documentation for - how to use CSS and Javascript in APEX.

thanks,
Deepak