Up-to-date alternative https://github.com/RadValentin/postcss-prefix-selector

PostCSS Prepend Selector

PostCSS plugin Prepend selector for each rule.

.foo {
    /* Input example */
}

.foo, .bar {
    /* Input example */
}

.selector .foo {
  /* Output example */
}

.selector .foo, .selector .bar {
  /* Output example */
}

Usage

postcss([ require('postcss-prepend-selector')( { selector: '.selector ' } ) ])

See PostCSS docs for examples for your environment.