• Rollup Version: 2.48.0
• Operating System (or Browser): MacOS 11.3 / affects all browsers
• Node Version (if applicable): run on 12.16.1 and v14.16.0
• Link to reproduction (IMPORTANT, read below): https://github.com/TheMcMurder/rollup-test

Expected Behavior

CSS is bundled into the output. The dependencies specify their side effects with: sideEffects: ["*.css"]. See package json files for button, theme, and provider

Actual Behavior

CSS is not bundled into the output

I'm happy to help solve this issue but I'm not certain where in rollup the issue lies. I found some test cases here but am not entirely certain where I would add another test case.