在angular 6中，你必须在src/style.css中添加only代码>(而不是angular.json):

In angular 6 you have to add only in src/style.css (instead angular.json):

@import "assets/plugins/listtyicons/style.css";
@import "assets/plugins/jquery-ui/jquery-ui.min.css";
@import "assets/plugins/bootstrap/css/bootstrap.min.css";
@import  "assets/plugins/plugins/isotope/isotope.min.css";

在angular.json

"styles": [
          "src/styles.css"
        ]