Minimum Package Manager sidebar width feels too wide when only default registries are present

Steps to reproduce:

1. Open the Package Manager (Window>Package Manager)
2. Drag the sidebar to its minimum size

Desired result: the sidebar does not get narrow enough when only default registries are listed. There is a lot of grey space between the end of the longest title and the right border of the sidebar. It's probably hard to guess the perfect minimum size, but it would be great to either reduce it or, ideally, to allow the user to collapse this sidebar altogether.