CSS and HTML When HTML was first created, style properties were defined directly in the code. However, rather than just adding more and more tags to HTML, the W3C introduced Cascading Style Sheets to fill the design void in straight HTML, allowing the Web to become semantic in structure. For example. In HTML, the strong tag does one thing and one thing only: It makes text “stronger,” usually by making it bolder. However, using CSS, you can “redefine” the tag so that it not only makes text bolder, but also displays text in all caps and in a particular font to add more emphasis.