Just have to dive into it. Books are boring but have one handy for a reference. You can pretty much find any topic you need by a Google search. Look at other people's code to get ideas of how to do it.
I don't recommend this but here's how I learned it. My first PHP project was on Rentacoder and I struggled through it until the point the buyer ran out of patience and got his money back through an arbitration. HOWEVER, I learned a lot and did get a partial payment for the product. It got me started but I would not recommend doing it this way unless you like to take big risks.
I fail to see how CSS is anything to do with knowing programming languages :P.
I learnt PHP, from websites, books & the manual - I also learn other languages at college. Looking through others work is all well and good but I find if you don't know what your doing at first you can easily miss interpret things, and fall into bad coding habbits.
It's best to learn everything from all sources available to you.
my resources:
-php manual
-php-general [at] lists.php.net
-internals [at] lists.php.net
-phpclasses.org
-some books and articles made by core php developers