Test expressions involing brackets #621
Description
E.g. (1rem + 1vw) * 2 - in context e.g.: font-size: clamp(2.5rem, (1rem + 1vw) * 2, 4rem);.
We need to know if these are parsed correctly, or there is some work to be done.
Also need to check the spec for what is or isn't allowed (for logging invalid constructs - see #462, #463, #596).
Relates to #389.