Base theme is missing blocks other themes contain #215
Description
And bunch of other things. There should be one neutral theme, that uses just the build-in HTML elements, no styles, just plain elements and inline JS (modals - dialogs), so we can see everything that needs to be modified, when creating custom theme. Just like Symfony has for forms. It doesn't need to be pretty, but it needs to be there as the simplest/minimal representation to have data table be usable.
Using Bootstrap or Tabler theme as a base is not really possible. We can't just include it and then work our way, styling and seeing all changes. It's bloated for that purpose (not that it's bad, but has Bootstrap related things, which are not helping out).