[V4] nesting rules doesn't behave well for pseudoelements and parts

[lucax88x]

What version of Tailwind CSS are you using?

For example: v4.1.5

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

For example: Vite 6.3.0

What version of Node.js are you using?

For example: v22.0.0

What browser are you using?

For example: Chrome, Firefox

What operating system are you using?

For example: macOS

Reproduction URL

https://stackblitz.com/edit/lit-element-ba85x7bn?file=src%2Findex.js,index.html,package.json

Describe your issue

In dev mode, so with nested css, there's a breaking change IF we use parts AND pseudo elements.

In the reproducion url you can see that if I do

my-element::part(text)::after {}

the pseudo elements works fine

but if I do

my-element::part(text) {
        &::after {}
}

the pseudo element doesn't show up.

Now, to be clear, this looks like a chrome/firefox bug/limitation/something but indeed, just wanted to raise for those people having the same issue.

might be related also to #16418

[philipp-spiess]

Hey! Thanks for that. I think too that this is related to #16418, so going to merge this together for now.

[lucax88x]

@philipp-spiess I created a duplicate because the bug happens also on firefox, but up to you!