Customize Nextcloud 'shared file' page. How best do this?

I would like to customize the page Nextcloud uses to share files and I’m not sure if this is possible, or the best way to achieve this.

When I share a file, to a a person without user account, by sending the person a shared link, the person then comes to (what I call) a share page. This share page is white background and the top border with my set colors on it.

I would like to add a ‘no right click’ functionality (a script) to this page. And I would like this functionality to always get included on every share page, no matter what file I share.

Yes, I know there are alot of opinions about this, but I still wish to see if it can be done.

Since this ‘share page’ looks the same way every time I share a file, I imagine that all share pages are generated from a template file, or some type of origin which could be changed. Changed by putting a JavaScript into the source code of the template file.

Is my understanding of how the share page is generated more correct than incorrect?

If I think very incorrect about this, is there a more suitable way to try to modify the character of the share page in such a way that a no right click function is always included?

I use Nextcloud off of a hosting service, so I don’t have as direct access to the config files as you may have if you run your own server. But the hosting service have a great support, so I may have to explain to the hosting company how they might try and do this.

Also, the sharing page is always white in background, while I always use the dark theme. Is there a way of making all share pages have a darker background?

Thanks for any input