The CSS files are in the theme folders and generally needs to be altered only if the entire contents of any filed is not visible.
The form field width is set in the from template codes along with the field size.
If you are using FireFox / Chrome browsers, use the FireBug extension and locate the code behind the places you wish to change and then search for the html snippets in FA codebase and alter as desired.
If you wish to seek professional help, post your needs (referring this post) in the jobs section of the forum. You may also contact the support partners listed in the Wiki.