Less
Less is a dynamic preprocessor stylesheet language that extends CSS with features like variables, mixins, functions, and nesting, which compiles into standard CSS. It allows developers to write more maintainable and reusable stylesheets by adding programming-like capabilities to CSS syntax. Less runs on both the client-side (in browsers via JavaScript) and server-side (using Node.js).
Developers should learn Less when working on large-scale web projects where CSS maintenance becomes cumbersome, as it enables variables for consistent theming, mixins for reusable code blocks, and nesting for cleaner selector hierarchies. It's particularly useful in front-end development workflows integrated with build tools like Webpack or Gulp to automate compilation, improving productivity and reducing CSS bloat.