CSSO (CSS Optimizer) is a CSS minimizer unlike others. In addition to usual minification techniques it can perform structural optimization of CSS files, resulting in smaller file size compared to other minifiers.

Minification (in a nutshell)

Safe transformations:

• Removal of whitespace
• Removal of trailing ;
• Removal of comments
• Removal of invalid @charset и @import declarations
• Minification of color properties
• Minification of 0
• Minification of multi-line strings
• Minification of the font-weight property

Structural optimizations:

• Merging blocks with identical selectors
• Merging blocks with identical properties
• Removal of overridden properties
• Removal of overridden shorthand properties
• Removal of repeating selectors
• Partial merging of blocks
• Partial splitting of blocks
• Removal of empty ruleset and at-rule
• Minification of margin and padding properties

The minification techniques are described in detail in the detailed description.

Authors

• initial idea — Vitaly Harisov (vitaly@harisov.name)
• implementation — Sergey Kryzhanovsky (skryzhanovsky@ya.ru)
• english translation — Leonid Khachaturov (leonidkhachaturov@gmail.com)
• japanese translation — Koji Ishimoto (ijok.ijok@gmail.com)

Feedback

Please report issues on [Github] (https://github.com/css/csso/issues).

For feedback, suggestions, etc. write to skryzhanovsky@ya.ru.

License

• CSSO is licensed under MIT