PHP is a Hypertext Preprocessor. This essentially means that PHP dynamically writes web pages for you. So it can query a database and print a report from it, or change CSS and such based on specific criteria.
elseif statements allow you to check to see if any of a number of conditions are true before failing out to the else in an if statement.
You can assign CSS attributes to HTML features using ID’s like you would with Classes. idStyle.css id.html