[Document Viewer] Left navigation pane UI not visible when PDF is loaded

When a PDF file is opened in the Document Viewer example, the left pane which can be used to navigate the PDF looks empty but it is clickable. 

Steps to reproduce:

1. Run the Document Viewer example
2. open a PDF file with more than 1 page

Actual Result:

PDF page preview is visible

Expected Result:

There is no preview of any PDF page

Reproducibility: 100%