Dropdown icon for all dropdowns are missing under Output Node (eg. Cube Output, Point Output, Octagon Output, Triangle Output) from Context category

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. Project > New VFX > Open
5. New VFX > Right-click > Create Node > Cube Output OR Point Output OR Octagon Output

Actual Result:
Dropdown icons are missing

Expected Result:
Dropdown icons are available and visible clearly

Reproducible in:
2020.1.0a9, 2020.1.0a8, 2019.3.0b7, 2019.3.0b6

Working fine on:
2020.1.0a7, 2019.3.0b5, 2019.3.0a10

Package version found: 7.1.2, 7.1.1.

NOTE:
Visual Effect Graph is introduced in 2019.3.0a10.

Environment:
Windows 10 & macOS 10.14