tailwindcss and shadowDom something break from 8.0.0-beta.13 to beta.14/15

[vdegenne]

I want to open a post before an issue because I'm not sure what's going on. Don't even know where to start to debug the issue... but

• 8.0.0-beta.13 my code works
• 8.0.0-beta.14 something breaks
• 8.0.0-beta.15 now no error anymore but some tailwind styles doesn't work anymore in shadow dom

reduced.mp4

(sorry but the commands are at the very bottom so the video controls could hide, you can download the video using the more button)

[travisbreaks]

Two changes between beta.13 and beta.14 that likely interact with your Shadow DOM setup:

First, beta.14 bumps Rolldown from rc.3 to rc.4, which changed chunk merging behavior. There's a known regression in beta.15 (#21826) where CSS that was previously emitted as a single stylesheet started splitting into multiple <link> tags. If your injection mechanism expects a single CSS bundle, it'll only capture part of the styles.

Second, beta.14 updated the IIFE detection regex for CSS injection (commit 5003de6). If your build uses IIFE or UMD format, the injection helper could be landing in the wrong spot.

Quickest way to isolate: add "overrides": { "rolldown": "1.0.0-rc.3" } to your package.json while keeping Vite at beta.14. If that fixes it, it's the Rolldown chunk splitting and should be filed on rolldown/rolldown.

For Shadow DOM CSS injection that works today regardless: import styles from './styles.css?inline' and use unsafeCSS(styles) in your Lit component. Bypasses Vite's injection entirely.