Hey guys! The Landing Page and the other templates aren't coded to adapt to the theme - they basically override Bootstrap's theme and force a color, which is why the dropdown doesn't work.
The Bootstrap themes that are built-in Bootstrap Studio are taken from Bootswatch - they are distributed as modifications merged with Bootstrap's css file and we've included them in the same way.
As for the Custom Code component, we delayed it for the upcoming release. See more here.