Anyway, people may visit this thread so it needs a good answer.
Here it is:
Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language like HTML. CSS is a cornerstone technology of the World Wide Web, alongside HTML and JavaScript.
CSS is designed to enable the separation of presentation and content, including layout, colors, and fonts. This separation can improve content accessibility, provide more flexibility and control in the specification of presentation characteristics, enable multiple web pages to share formatting by specifying the relevant CSS in a separate .css file and reduce complexity and repetition in the structural content.
Separation of formatting and content also makes it feasible to present the same markup page in different styles for different rendering methods, such as on-screen, in print, by voice (via speech-based browser or screen reader), and on Braille-based tactile devices. CSS also has rules for alternate formatting if the content is accessed on a mobile device.
The name cascading comes from the specified priority scheme to determine which style rule applies if more than one rule matches a particular element. This cascading priority scheme is predictable.
Also get some little-known facts about CSS:- The color Property Isn’t Just for Text;
- The visibility Property Can Be Set to “collapse”;
- All CSS galleries blocked
essay writing services in usa from submitting their design;
- The clip Property Works Only on Absolutely Positioned Elements;
- Vertical Percentages are Relative to Container Width, Not Height;
- The text-decoration Property is Now a Shorthand;