The problem is simple, and shows between the two attached screenshots.
- On a light theme like 'Default', containers (folders etc.) always show that they are such via their expansion arrows, even when they're selected
- But with a dark theme, the expansion arrows disappear, don't show in contrasting light color, when a container is selecdted
- Thus, you don't see that it is a container, may well fail to open it unless you click where the arrow hides, and thus can 'lose', find yourself unable to access the contents, even when you may know it's there.
In these examples, the container is open, so you see the content, but if it is closed, there's no indication with a dark theme that it's even there, when you have the container selected.
This example is with Solarized Dark, but the problem seems to be the same with other dark themes.