Add margin to block-level math

[pepelsbey]

⚠️ There’s a PR that enforces block rendering for all block-level math. They should be merged together.

Summary

It adds margins for block-level math:

<math display="block">
  …
</math>

The same margins as <p> and <pre> have.

Problem

Block-level math, rendered outside of paragraphs, doesn’t have margins:

Solution

Now it does:

math[display="block"] {
  margin: 1rem 0 2rem;
}

[fiji-flo]

Doesn't break anything and safe to merge even without the content PR

[pepelsbey]

Thank you!