Compiling multiple CSS into ONE CSS with Laravel MIX
The solution was to import all the required css into one main css file, then use that inside the mix chain:
in app.css we import all of our css files
@import 'resources/css/plugin-1.css';
@import 'resources/css/plugin-2.css';
inside webpack.mix.js we use resource/app.css as an input
mix.styles([
'resources/app.css',
], output);