If you only want to tinker with certain aspects of the component but like to keep the CSS in sync with future package updates, nothing stops you from overriding only certain CSS rules with your own tweaks. Every DOM-element of the component has a class with prefix media-library.
Let's say your thumbs aren't square and you want to show them in their original aspect ratio.
Inspect the component in your browser to find out that the thumbnail is rendered in the DOM element with class media-library-thumb-img. Next, write some extra CSS for this class:
If you want to go full-option, you can always copy src/styles.css to your own project and go wild.
In this example we renamed the file to custom/media-library.css.
Beware: you will have to manually keep this CSS in sync with changes in future package updates.