What version of Tailwind CSS are you using?
3.4.0

What build tool (or framework if it abstracts the build tool) are you using?
CDN

What version of Node.js are you using?

CDN, so N/A

What browser are you using?

Chrome

What operating system are you using?

Windows

Reproduction URL

We identified the offending CSS in #12627 (comment)

3.3.7:

.dark .dark\:bg-neutral-700 { ... }

3.4.0:

:is(:where(.dark) .dark\:bg-neutral-700) { ... }

If the :where() pseudoclass is removed, everything starts to look the same.

Describe your issue

Dark mode is broken.