I'm unable to use almost any of your plugins SCSS files as imports in my main SCSS file.
Let me make an example. In file
node_modules/@syncfusion/ej2-calendars/styles/calendar/bootstrap4.scss contents are:
@import 'ej2-base/styles/bootstrap4-definition.scss';
@import 'ej2-buttons/styles/button/bootstrap4-definition.scss';
@import 'bootstrap4-definition.scss';
@import 'icons/bootstrap4.scss';
@import 'all.scss';
There is no ej2-base folder relative to this file, so that is an incorrect syntax/path. As you are already using @synfusion alias, I think you should prepend that to all such import statements, which are pointing to separate packages.