Support "Pure" scope as in CSS-loader

[StarpTech]

As titled. https://github.com/webpack-contrib/css-loader#scope

This would allow to have real "No global scope." for CSS modules.

Example:

Syntax error: Selector ":global .page" is not pure (pure selectors must contain at least one local class or id)

  17 |   pointer-events: none;
  18 | }
> 19 | :global .page {
     |                                             ^
  20 |   width: 4px;
  21 | }