CSS container query unit support

[bernesto]

Can we add support for CSS container queries.

Currently throws warnings for container query length units:

cqw: 1% of a query container's width
cqh: 1% of a query container's height
cqi: 1% of a query container's inline size
cqb: 1% of a query container's block size
cqmin: The smaller value of either cqi or cqb
cqmax: The larger value of either cqi or cqb

(https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_container_queries#container_query_length_units)

[jakubpawlowicz]

We can. Those need to go into validator.js here - https://github.com/clean-css/clean-css/blob/master/lib/optimizer/validator.js#L338

[bernesto]

I submitted a pull request.

This may be more complex: I also notice that it strips out classes wrapped in @container queries such as this:

@container sidebar (min-width: 700px) {
  .card {
    font-size: 2em;
  }
}`

[jakubpawlowicz]

Thanks @bernesto! For @container, please check if you use an older version of clean-css, as it seems to work OK with clean-css 5.3.2, see here: https://clean-css.github.io/