.less File — Less CSS Preprocessor

Less (Leaner Style Sheets) is a CSS preprocessor that extends CSS with dynamic features including variables, mixins, operations, and functions. Created by Alexis Sellier in 2009, Less uses a syntax that is a superset of CSS — all valid CSS is valid Less. LESS files add variables (@color: #333), parametric mixins for reusable style blocks, nested rules for clearer selector hierarchies, mathematical operations on values, and functions for color manipulation and string operations. Less can be compiled to CSS server-side using Node.js or client-side in the browser using less.js. Less gained significant adoption as the CSS preprocessor used by Bootstrap (versions 2 and 3), making it one of the most widely used preprocessors during the early-to-mid 2010s. Bootstrap 4's switch to Sass shifted the community balance toward SCSS, but Less remains maintained and used in existing projects, particularly those in the JavaScript ecosystem. Less's simpler feature set compared to Sass (no control directives like @if/@for in early versions) made it easier to learn but somewhat less powerful for complex scenarios. The lessc compiler and webpack less-loader provide build integration.