Add support for @layer

[pvcresin]

Corresponding Issue(s):

• Support @layer property #1634

What Would You Like to Add/Fix?

Add support for @layer
See more: https://developer.mozilla.org/en-US/docs/Web/CSS/@layer

Implemented with reference to ConditionalRule and @container PR.

Perhaps this change does not support all @layer features, but I would like to be able to use just some of them.

Todo

• Add test(s) that verify the modified behavior
• Add documentation if it changes public API (not changed)

Expectations on Changes

Changelog

Added support for @layer.

[JuhG]

hey @kof, any chance you could take a look at this? thanks!