The CSS language (cascading style sheets) is a language that defines the appearance of a document written in HTML language. This is how the elements of the web page created with HTML can be given the desired appearance.
Using CSS, you can modify colors, spaces between elements, fonts, etc.; all with the intention of separating the structure of the presentation.
This separation between the structure and the presentation is very important, since it allows that only by changing the CSS the aspect of a web page is completely modified.
This provides a lot of flexibility and speed as users can use custom style sheets. Through the style sheets we improve web accessibility and the way in which we structure the contents, which is why it helps us to improve the user experience.
The programming language PHP (Hypertext Preprocessor) is a language used to program scripts on the server side and which are embedded within the HTML code of the page.
This language has a large library of functions which provide a lot of flexibility to web pages, in addition to being very fast, it improves the loading speed of the sites.
A server-side language is one that runs on the web server, just before the page is sent over the Internet to the client, the pages that run on the server can perform access to databases, network connections, and other tasks to create the final page that the client will see.
The client only receives a page with the HTML code resulting from the execution of the PHP. Since the resulting page contains only HTML code, it is compatible with all browsers.