The css selector is right above it. .table-container .t ...
If you dont want to change it in every table like @cmallonee suggested, then you could change it with css in a theme using that selector with a new padding.
If you dont have the theme module and dont want to get it just for this you can also 'inject' it in a styleclass like i showed here:
something like this should work on all tables:
}.table-container .t .tc .content {
padding: 5px;
}{
note that doing this will remove the option of changing padding on individual level on other tables