Custom CSS outputting HTML entities instead of correct characters

[megmorsie]

Describe the bug

I compared to a fresh WordPress install to verify, it seems like it's only happening on WordCamp sites. The > symbol is being output as > in the customizer CSS output.

To reproduce

Steps to reproduce the behavior:

1. Log into a WordCamp site with admin access.
2. Click on Customize > Custom CSS.
3. Enter CSS with > selector.
   My example uses:
   #subscribe-submit > button { background: gray; }
4. Notice preview updates.
5. Publish & look at Customizer output in inspector, > is replaced with >

Might be related to #574?

Expected behavior

I would expect the output to have > since it's a proper CSS selector. Or if it must be sanitized out, showing an error message or something to indicate that it's not an allowed character would be nice.

Screenshots

I made a screen recording comparing the WordCamp site with a fresh WP install.

WordCamp

Noticed on NEO but I'm guessing other sites have the same issue.

System (please complete the following information):

• Device: MacBook
• OS: MacOS
• Browser: Firefox
• Version: 86.0.1

[CdrMarks]

This also affects the make.wordpress.org network (per Dion).

I opened Automattic/jetpack#21603 earlier today.

[CdrMarks]

The Remote CSS Plugin can be used as a workaround if needed. I tested it on Birmingham 2022 and was able to see > show as the symbol.