[css-counter-styles-3] `@counter-style` declared with extended `system` and `*-symbols`

[cdoublev]

https://drafts.csswg.org/css-counter-styles-3/#valdef-counter-style-system-extends

If a @counter-style uses the extends system, it must not contain a symbols or additive-symbols descriptor, or else the @counter-style rule is invalid.

In Chrome/FF (at least), the rule is valid and does not define a counter style.

<style>
  @counter-style counter {
    system: extends cyclic;
    symbols: foo bar;
  }
  ul { list-style: counter }
</style>
<ul>
  <li>one</li> <!-- 1. one-->
  <li>two</li> <!-- 2. two -->
</ul>
<script>
  document.styleSheets[0].cssRules.length // 2
</script>

At least, considering their related issues/resolutions, I think invalid may be an oversight in 4068d10 / ba2a8cb.