Certain themes and plugins hidden from users but network admin can activate

I’m sure this question must have come up before I just haven’t found it anywhere.

Firstly, I would like to find out how to remove certain themes- for example, I will have a parent theme that is a framework and I will child themes for the parent theme. If my users select a theme I don’t want the (framework) parent theme visable. Another example would be there is a child theme that I will design specifically for my multi site homepage so I only want this theme visible to the admin and not for all other users.

Secondly, the same type of question but for plugins – There are some plugins that I only want the network admin to be able to activate & use that are hidden from other users.

Is there some type of plugin that allows this or would you recommend to inspect element of the themes and plugins that I don’t want users to see and then display:none; in the CSS (After admin has activated them) .

Thanks