PostCSS plugin to minify CSS using CSSO (a CSS minifier with structural optimizations). Under the hood, the plugin converts PostCSS AST into CSSO's AST, optimises it and converts back. The plugin uses input PostCSS's AST nodes (or their clones) on back convertation, so the shape of original PostCSS's nodes persists the same after compression in most cases (e.g. properties added by other plugins isn't lost). This approach makes it possible to achieve a great performance and generate source maps correctly.