Structuring Imports and Startup files

Can someone please explain this in detail with example. ?

Actually I was finding a way to load css js files in a particular order. And in example above all the files are imported in “imports/startup/client/routes.js” and then routes.js is imported in index.js.

I’m a little bit confused here. Aren’t the files loaded twice this way ? And how should I import the JS and CSS files in correct order ?