CSS styling over MathML Core

[dginev]

Description

This proposal seeks to improve interop of CSS styling over MathML Core elements.

The relevant browser tests are hosted at:
https://wpt.fyi/results/mathml/relations/css-styling?label=master&label=experimental&aligned&q=math%20%20not%28path%3A%2Fjs%29

This issue follows up on last year's proposal in #556, which was framed in a very narrow scope. That proposal is still on topic today. We want to attempt a more general framing this year.

A sibling proposal is offered in #787 , which focuses on the native tagsuite of MathML Core. This issue has a separate focus area, solely requesting interop for CSS styling over MathML.

Specification

https://w3c.github.io/mathml-core/#css-styling

Additional Signals

The proposal has the support of the W3C Math Working Group.

Interoperable CSS support for MathML will aid large scholarly web resources, such as Wikipedia and arXiv, in providing high-quality rendering of mathematical syntax to our readers.