as far as i know you should use PHP for dynamic content loading and CSS for the Layout as you already did. I even dont know (at once) a method to load "text" content through CSS Files, but i am sure if you search for it you will find it.
What you could also do is to combine CSS (Layout) + HTML and JavaScript/jQuery to refresh the Pagecontent without reloading the whole Page everytime something has to change. Thats the common way "I" know.