Cascading Style Sheet / Development Terms Cascading Style Sheet A Cascading Style Sheet, commonly known as CSS, is a stylesheet language used to control the visual presentation of HTML elements on a webpage. CSS defines how content should look across different devices and screen sizes, including layout, fonts, colours, spacing, and animations. While HTML provides the structure of a webpage, CSS determines its style. The term “cascading” refers to the way styles are applied in a hierarchical order, allowing for rules to override one another based on specificity and location. CSS can be applied in three main ways: inline (within an HTML element), internal (in a style tag in the HTML document) or external (linked in a separate .css file). External stylesheets are the most common approach, as they allow for cleaner code and consistent styling across multiple pages. CSS also supports media queries, which enable responsive design by adapting the layout based on screen width or device type. This flexibility is essential for delivering accessible and mobile-friendly web experiences. Modern CSS supports a wide range of features that enhance both usability and performance, including variables, grid and flexbox layout systems, pseudo-classes and custom animations. Clean, well-structured CSS improves website accessibility, speed and search engine performance by ensuring that content is readable, properly formatted and easy to navigate. It also helps designers and developers maintain consistency and reduce development time. Whether you are updating brand styles, creating user interface components or optimising for dark mode, CSS is a foundational tool in modern web development.