The two most important languages for web design are CSS and HTML. Many people use these two languages equivalently, but they are actually very different. Here is a brief explanation of the difference between the two languages: HTML is a markup language used to create the structure of a page. It determines where each area is located on a page. CSS is a programming language used to design the appearance of a page. It thus determines the appearance of individual elements on a page, for example, color, font and size.