CSS is a computer language used to style webpages. It stands for Cascading Style Sheets and is used to control the appearance of the elements on a webpage. It is connected with HTML in that HTML controls the structure of the web page and CSS controls the look. CSS can control the layout of multiple web pages all at once by changing one line of code. CSS also helps to make webpages more interactive and responsive by allowing for dynamic stylings such as rollover effects, animations, and transitions. CSS can also be used to customize fonts, colors, spacing, and other aspects of design. CSS is used to improve the accessibility and usability of webpages, making it easier for people with disabilities to use the web. CSS is also used to create mobile-friendly webpages and optimize webpages for search engine optimization. CSS is an essential component of any website and is critical for making webpages look attractive, professional, and easy to use.