PostCSS plugin to place rules directly at the root node.

The @at-root causes one or more rules to be emitted at the root of the document, rather than being nested beneath their parent selectors:

.parent {
  ...
  @at-root{
    .child {...}
  }
}

Which would produce:

.child { ... }
.parent { ... }

It will play well with postcss @include plugins.
foo.css:

@at-root {
  @viewport { width: device-width; }
}
.foo {
  color: blue;
}

bar.css:

.bar {
  @import "foo.css";
}

Will produce:

@viewport { width: device-width; }

.bar .foo {
  color: blue; 
}

postcss([ require('postcss-atroot')() ])

See PostCSS docs for examples for your environment.