I believe that the problem come from these line

@import "~font-awesome/css/font-awesome.css";
@import "~bootstrap/dist/css/bootstrap.css";
Your prod source code cant find node_modules folder contain these 2 package. So I would suggest you include css in your angular.json something like this

"styles": [
    "node_modules/bootstrap/dist/css/bootstrap.min.css",
    "node_modules/font-awesome/css/font-awesome.min.css"
],