You are not in danger of spamming but you are in danger of being less than efficient.
The different search engines have different tecniques (and some ignore keyword meta tags) but it is generally not useful to keep repeating any word or term. You said CSS once, that should be enough. Tutorials, that's a differnt word, so it should be there.
Pay attention to the titles on your pages and make sure the density of the terms you want to be known for is high (ie, how many times does the word CSS appear on the page? )Twice in a 100 word page? You may want to insert CSS into the text a couple more times. That would help your ranking with most search engines more than repeating it in the meta tags.
CSS is a tough term to be known for. There's lot of competition.