Percentage opacities in CSS files will compile to "1%" in a production build

Created by: bvaughn

Originally reported by @mruiz42: https://github.com/facebook/react/issues/19747

• Source code: https://codesandbox.io/s/trusting-glitter-0icl7
• Deployed sandbox: https://csb-0icl7.netlify.app/

Recap of the problem, courtesy of @eps1lon:

What a frustrating bug. It originates in react-scripts (reported in https://github.com/facebook/create-react-app/issues/7980). It seems like the underlying fix wasn't propagated. If you go further down you find https://github.com/NMFR/optimize-css-assets-webpack-plugin/issues/118 and https://github.com/cssnano/cssnano/pull/881.

I'd suggest tracking down which package didn't publish the fix by upgrading their relevant dependencies.

Maybe @gaearon can move this issue to create-react-app. Otherwise we should file a new bug report with create-react-app and close it here.