What is CSS (Cascading Style Sheet)?

CSS, or Cascading Style Sheets, is a programming language used to create great-looking web pages beyond plain and uninspiring blocks of text. It allows you to apply styles to HTML documents by prescribing colors, fonts, spacing, and positioning. CSS can be reused across multiple HTML pages, improves SEO, and allows for offline viewing. If HTML is the very foundation of a site, CSS is all of the aesthetics of an entire website.