Issue with nested css linting support (follow-up to #33)

[julienw]

After #33, #64, #51 were fixed, I found that there's still an issue with nested css.
Nested selectors such as .page-nav-icon + & { don't seem to work.

See the project https://github.com/julienw/csstree-bug-33
Run npm i && npx eslint, it errors on line 12.

[nzakas]

@julienw please be sure you're providing a full description when you file issues. Otherwise it takes us more time to have dig through things. Thanks for your consideration

---

To clarify, here's a complete example that doesn't parse correctly:

slot {
  margin: 0;
  padding-inline-start: 0;
  user-select: none;

  @media (max-width: 52rem) {
    display: inline-block;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;

    .page-nav-icon + & {
      display: none;
    }
  }
}

This errors on line 12. However, this seems to be related to the @media being present and not the .page-nav-icon + & alone, because the following code works fine:

slot {
  margin: 0;
  padding-inline-start: 0;
  user-select: none;

    display: inline-block;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;

    .page-nav-icon + & {
      display: none;
    }
}