Customize Function not Working (Hemingway Rewritten)

The customize side-bar menu with all of the various sections (site title & tagline, colors, logo, etc.) is frozen. I can’t access any of the tabs. Any idea how to fix this? It worked when I first downloaded the theme, but has been frozen ever since.

If not, is there another way to customize font colors?

Here’s a screen grab for reference: https://snag.gy/MnBO8.jpg

Thanks.