TL;DR Namespace CSS to AngularJS component by styleUrl property using component name.
We need to scope all CSS styles with a class whose name is equals to component name. (Note that component name is camelCase and class name is kebab-case.)
a-foo {
  .class { ... }
  ...
}const AFooComponent = {
  selector: 'aFoo',
  styleUrl: './a-foo.css'
  template: '...',
};
angular.module('...', [])
  .component('aFoo', AFooComponent);