The scroll bar is missing for the detailed view of packages.

Steps to reproduce:
1) Create a new project
2) Window > Package Manager.
3) Select a package with long description e.g. AI Planner

Actual result: The scroll bar is missing for the detailed view of packages which makes Install/Remove button invisible.

Expected result: Scroll bar is available for Packages with a long description.

Occurring in: 2019.3.0a10
Not reproducible on: 2019.3.0a9, 2019.2.0b10

Environment:
Windows & Mac.

Workaround:
1. Rescaling window gives access to all the hidden information/functionality.
2. The docked package manager window can be maximized to access all the information/functionality.