Corporate Theme (light blue) - Three index page widgets re-sizing issue


I have installed the corporate theme in light-blue to my site:

I want to change the size of the three home page widgets so that they are all of equal size.

I changed this in the custom.css sheet, which resize them but the padding remained the same (even after trying to change that) which caused the third widget box to go down to the next line.

I also would like to change the background color of the "Blog Welcome Msg" box -- which stylesheet would I do that in?

Thanks in advance.