Not every Drupal contributor sharing a theme on drupal.org is a whiz at cross-browser CSS or even knowing where to begin. A collection of tips and guidelines for contrib themers would be helpful so people know where to turn for browser testing resources.

Deliverable:
Handbook page in theming section that includes:
- basic CSS coding principles -- valid code that follows standards (http://drupal.org/node/769692) will help start you on the right foot
- what browsers your theme should aim to support -- link to current percentage market share
- how to test locally for different browsers (IE collection, virtual machines, and just installing other browsers in the first place)
- external services to help you test themes in different browsers

Resources:
http://www.w3schools.com/browsers/browsers_stats.asp
http://www.lofitrading.com/15-highly-useful-resources-for-cross-browser-...
http://jpedroribeiro.com/2010/06/cross-browser-testing-resources/
http://finalbuilds.edskes.net/iecollection.htm