What is CSS and how is it used

CSS, an acronym for Cascading Style Sheets, is the language used to define the visual appearance of web pages. While HTML structures the content, CSS determines how that content is presented: colors, typography, spacing, sizes and the positioning of elements. The term “cascading” refers to the mechanism through which style rules are applied according to priority, allowing general styles to be overridden by more specific ones. This approach makes it possible to clearly separate the structure of a page from its presentation, making the code more organized, maintainable and reusable for projects of any size.

Introduced by the W3C in 1996, CSS has evolved over time through several versions up to the current CSS3, which brought advanced features such as animations, transitions, gradients and native variables. Layout technologies like Flexbox and Grid have particularly revolutionized the way developers build interfaces, making it much easier to manage complex structures adaptable to different screen sizes. The ability to write responsive CSS, capable of adapting fluidly to mobile devices, tablets and desktops through media queries, has become an essential skill in modern web development, to the point that designing first for mobile devices and then for desktops is now considered the industry standard practice.

Despite its apparent simplicity, CSS can quickly become complex to manage in large-scale projects, where overlapping rules and selector specificity may generate unexpected behaviors that are difficult to debug. For this reason, several tools and methodologies have emerged over time to organize it more effectively, such as preprocessors like SASS and LESS, which add features such as variables, functions and nested rules, or architectural approaches like BEM and SMACSS. Together with HTML and JavaScript, CSS forms the fundamental triad of front-end development, and mastering it deeply, beyond the basics, is what distinguishes a developer capable of building solid and professional interfaces from someone who merely assembles working pages that become difficult to maintain over time.