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Changing 1 line in the file themesource > datawidgets > web > main.scss, Line 1:
1 @import "../../../theme/styles/web/sass/main";
something like the above may help you.
Hope it helps!
Please go to App directory and delete the folder and try to open the Application again.
May this help for you.
Please provide you found any alternative instead of this.
This issue occurs due to app directory being in network folder of computer. Download/Keep your app in drive location this will resolve automatically.