There is so many information about css in the internet but most of the stuff, is totally non-sense and is just misleading people into copy & pasting bullshit where they don't understand why it is are working.
This is one of the biggest issues of frontend design! Thats why so many designs/websites fail. Especially cross-browser.
It is just a little you need to know, to truely understand how css is working. I hope these informations from other wonderful authors help you to improve yourself and make frontend and css work less painfull