I would not recommend to use a HTMLSnippet for something like that, it's not very durable. And you will load javascript from a widget to load styling/html.
I would recommend instead to follow this learning path:
https://academy.mendix.com/link/paths/123/Style-your-App-with-Sass
It will give you insight how to view styling from your Mendix application (that's your question) and show how to adjust it to your preference. So you are more in control of your styling in your whole application instead of what you use now very specific parts (pages) of your application.
Good luck!