How do professional web designers create cross-browser CSS? Is it generally done by hand, or are there toolkits that can streamline the process, like YUI does for JavaScript? I'd prefer to stay away from WYSIWYG editors like DreamWeaver. Thanks!
It's generally done by hand.
It typically starts by applying a CSS reset to even the playing field.
And you should aim at standards compliant CSS and then only as a last resort apply hacks for IE (yes I just called it out).