Convert modern CSS into something browsers understand

PostCSS plugin to reduce calc()

Discard empty rules and values with PostCSS.

Minify at-rule params with PostCSS

Convert two value syntax for repeat-style into one value.

Normalize keyword values for position into length values.

Normalize unicode-range descriptors, and can convert to wildcard ranges.

Search CSS(-like) strings

Reduce transform functions with PostCSS.

Normalize CSS animation/transition timing functions.

Normalize URLs with PostCSS

Nest rules inside each other in CSS

Ensure CSS selectors are unique.

Merge longhand properties into shorthand with PostCSS.

PostCSS plugin to transform :not() W3C CSS level 4 pseudo class to :not() CSS level 3 selectors

Use the :focus-within pseudo-selector in CSS

SCSS parser for PostCSS

Trim whitespace inside and around CSS rules & declarations.

Use the :focus-visible pseudo-selector in CSS

Use unquoted format on @font-face CSS definitions.