No, you used PHP, Html and CSS. PHP simply sends html to the browser, your browser then interprets that html to make the page. And no, not all browsers work the same unfortunately.
@ dan-t: More definitively, when a browser (user) asks for a php page, the server (most likely apache) recieves the request. This file is in turn handed to the server-side php interpreter (due to the php extension in the file name), which in turn examines and executes the code within the php tags, and replaces this content with the end result (in the form of html), which is in turn handed back to the server, which is finally handed over to the browser with all php code parsed.
So depending on how old the browser is, and how old the code in the php page is, will determine any issues from that standpoint.. but as a rule, with a modernized browser and good clean up-to-date php code, there should be no issues. As for CSS, this is a different ballgame altogether, as CSS is not server-side technology.. this is entirely dependant on the broswer, and thus can have major ramifications if the user uses CSS code that the browser does not understand. It is fairly safe to code in CSS 2.1 these days, as most browsers support this... if you start using some CSS 3 code however, don't expect any smooth sailing anytime soon
Wow, most of that went over my head!
I don't even know what CSS 3 is.
But thanks for that info.