What is csso?

CSSO (CSS Optimizer) is a JavaScript tool that makes CSS files smaller. CSS is the language that controls the visual appearance of web pages, and CSS files can grow large as projects expand. Smaller files load faster for visitors, which is why developers typically run CSS through a minifier before publishing a website. What sets CSSO apart from simpler minifiers is that it does three levels of work. The first is cleaning: removing comments, extra whitespace, and rules that have no effect. The second is compression: replacing longer values with shorter equivalents, for example turning the color value #ff0000 into the word red, which takes fewer characters. The third is restructuring: merging separate CSS rules that target the same elements, combining duplicate property declarations, and reordering things where safe to do so. These structural changes can produce meaningfully smaller files than compression alone. The library works in Node.js and can also be loaded directly in a browser. You pass it a string of CSS and it returns a minified string. The API has options to disable the restructuring step if you want safer but less aggressive minification, to generate source maps (files that let browser developer tools show you the original unminified code even when the minified version is running), and to pass usage data that tells CSSO which selectors and properties are actually used in your HTML so it can remove the rest. Plugins and integrations exist for the common JavaScript build tools: Gulp, Grunt, webpack (as both a loader and a plugin), PostCSS, and editors like VS Code, Atom, and Sublime Text. There is also a command-line version called csso-cli for running it from a terminal without writing code. The README is detailed and includes code examples for every part of the API.