⚠️ PostCSS Selector Not was moved to @csstools/postcss-plugins. ⚠️
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postcss-selector-not

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

Installation

$ npm install postcss postcss-selector-not

Using this input.css:

p:not(:first-child, .special) {
  color: red;
}

you will get:

p:not(:first-child):not(.special) {
  color: red;
}