Back in PHP/CSS hell

I think one of the main reason why I like Ruby on Rail is the fact it
is a opinionated software. Unfortunately when it come to the design
(css) part you don’t get any guidance.

I have now spent quite some time, trying to find a good productive
approach that suit me.

I should be very interested in knowing how other Ruby on Rails
developers prefers to work with the design of your apps. I know many
do not do any design at all but you how do please share your
thoughts.

Do you use any CSS framework? Do you prototype directly in CSS or
using photoshop/fireworks? Do you use CSS3 classes for FF and Safari
and in that case how do you deal with the fallback for EE?

Do you have some good links to share where I can find good information
about working in a productive way using CSS?

Thanks and sorry for my poor English

I like Yahoo Developer Network

Thanks @Tom Ha
I have been looking at YUI earlier. I use Jquery and did find YUI a
bit of a overkill.
Do YUI offer some advantages over other CSS frameworks for example
Blueprint and Grid 960 ? It seems they do more or less the same
thing?