The opacity value was changed to 1% after building the Reacjs project
This issue has been reported in create-react-app and optimize-css-assets-webpack-plugin. https://github.com/facebook/create-react-app/issues/7980 https://github.com/NMFR/optimize-css-assets-webpack-plugin/issues/118 It appears the bug has been fixed, but the latest released version does not have the fix. I’ve fixed the problem by changing my opacity values from nn% to 0.nn values (e.g. 70% becomes 0.7).