good idea to first have a basic understanding of html and css before diving into javascript/jquery and php. having that said when you feel like jumping into other languages right now I would nevertheless encourage you to do it. because when you're passionate / interested about them this is the most important thing of all - at the end coding (in no matter what language) is fun ;)
in terms of css the only chapter I would recommend to look at (in general) would be media queries - in today's world with tons of different screen sizes this will be the key to responsive design (but that's just a tip of course).
hope that helps and keep enjoying learning ;)