CSS (Cascading Style Sheets) is a stylesheet language that is used to describe the presentation of a document written in a markup language, such as HTML. It is used to control the layout, colors, fonts, and other visual elements of a webpage.

CSS allows you to separate the presentation of a webpage from its structure, which is defined by HTML. This separation of concerns allows you to make global changes to the layout and design of a website by modifying a single CSS file, rather than having to make changes to each individual web page.

CSS is important because it provides a way to apply consistent styling to a website, making it more visually appealing and user-friendly. With CSS, you can control the layout of your web pages, change the colors, font size, background images, spacing and many more. It also plays a major role in accessibility and SEO, by providing a way to separate the content from its presentation and make the website more readable for people with disabilities and search engine crawlers.

CSS has become an essential part of web development, it’s the key of creating a polished and professional-looking website, with a consistent design, easy to read and navigate and optimized for different devices. Without CSS, web pages would be plain and difficult to read, and the look of a webpage would be inconsistent from one browser to another.