What are the main CSS preprocessors?

The most common CSS preprocessors:

1. Sass (SCSS syntax) The most popular and most developed preprocessor. Supports variables, nesting, mixins, functions, modules and advanced code-structuring features. SCSS syntax closely resembles plain CSS.

2. LESS Historically one of the first popular preprocessors. More often found in older or already existing frontend projects. Has capabilities similar to Sass, but is less flexible and develops more slowly.

3. Stylus Uses a minimalist syntax, allowing different styles of writing (with or without curly braces). Flexible, but less common than Sass.

These three are considered the basic and best-known preprocessors.