The separator between "Stop" and "Custom" button is missing under "VFX Event Tester" window in the Scene View, refer attached screenshot

Steps to repro:
1. Create a new project
2. Windows > Package Manager > Visual Effects Graph > Install
3. Project > right-click > Visual Effects > Visual Effects Graph
4. Hierarchy > create > Visual Effects > Visual Effect

Actual Result:
Separator between "Stop" and "Custom" button is missing

Expected Result:
Separator between "Stop" and "Custom" button visible clearly

Tested on Unity version:
2020.1.0a18, 2019.3.0f5

Package version found: 7.1.7, 7.1.5, 7.1.1, 7.0.0

NOTE:
Visual Effect Graph is introduced in 2019.3.0a10.

Environment:
Windows 10 & macOS 10.14