I have created html/css for modern browsers (IE7 and above, firefox, etc) and am good at it.
When I look into my html/css with ie6, there is always something wrong.
The fixes I create for it are usually ie6-specific (no problem though), and I usually don’t know exactly what caused the issue (or how I fixed it sometimes).
I want to become more knowledgeable about css (old and new).
What book/website do you recommend?
I’d recommend http://www.quirksmode.org
They say that:
‘QuirksMode.org is the prime source for browser compatibility information on the Internet.’