CSS stands for cascading style sheets, and as the name implies, it is a styling language turning a boring web page created using only a markup languages (HTML, SVG, or XML) into a better looking, pleasing to the eye page.
CSS syntaxes can be added to the document in 3 different ways:
Selecting the color of is an example of page styling is, anyway, other styling options are similar but with different syntax (you can explore more on w3schools).
For setting the color of a text you can use: