FieldGroup - Named Container oddity

[adam-enition]

I've been looking at this for a few hours, and to be honest, I still don't know if this is a skill issue, Shadcn issue, tailwind issue or Tanstack Start issue! 🤷‍♂️

When using the FieldGroup component I have noticed that on slower connections and sometimes on faster connections, the styling of child components seems to go a bit wonky for a split second. I can't seem to get it to do it for any of the Shadcn form examples so I have a feeling it could be a Tanstack Start/@tailwindcss/vite issue, but thought this might be a better place to see if anyone has seen it before.

This only happens when the class @container/field-group is present on the FieldGroup component. If I strip it out, the issue goes away.

The best way to explain is to show it - forgive the horrendous styling, but this shows it best. Keep an eye on the buttons on load:

2025-11-25.23-11-37.mp4

2025-11-25.23-13-55.mp4

This setup is using Tanstack Start + Tanstack Form + Tailwindcss Vite plugin.

The card components have named container classes, but these don't seem to affect any child components, including buttons.

Any ideas? Or anyone seen anything similar?