TailwindCSS styles not applied in Vite sandbox preview server

[btbrandon]

Description

I’m running a Remix + Vite + TailwindCSS app inside my custom “sandbox” runner (an Express + Vite dev server that copies my project into /private/tmp/... and spins up Vite there).

What I expected: Tailwind utility classes should be applied in the sandbox preview exactly the same as in my local IDE dev server or my production deploy.

What actually happens: In the sandbox preview, none of my TailwindCSS classes take effect—layouts collapse, maps don’t render full-height, component styles are missing, etc.

I get warnings even though the set up is correct:

warn - The `content` option in your Tailwind CSS configuration is missing or empty.
warn - Configure your content sources or your generated CSS will be missing styles.
warn - https://tailwindcss.com/docs/content-configuration

Reproduction

https://github.com/btbrandon/sandbox-bug-reproduction

Steps to reproduce

Set up steps in README

Linked issue from Vite

vitejs/vite#20553