Firefox seems to be the prefered browser to use when altering CSS etc.
I use Web Developer from this Link:
Web Developer
Just download the version for your browser, and install.
Once installed you can (for example) press
Ctrl +
Shift +
y
and just place your marker onto whatever area etc you want to see the details for.
It can also be used for a range of diverse things, but I'm not smart enough to understand it...
There is also a similar tool for Explorer that is apparently very good, iDev or something.
I installed it, but it was a bit too complex for me to get to grips with.