Linux display issue with the Terminal Block Generator window [Solved]

Hi,

I am using Ubuntu 18.04 with the i3 window manager. It might be my setup which causes the issue, but there might be some software configuration to have it fixed.

EDIT:
modifying the background variable in my ~/.Xresources file helped, file change:

!! *background:       #1b1918 !! dark background, now commented
*background:       #ededed !! gray background, now in use

The problem: The contents of the plugin window are not visible. Screenshot is attached.

The button "Create Terminal Block" becomes visible though every time I hover over it with a mouse.

Do you have some recommendations for potential fixes? Could it be PySimpleGUI which causes the issue?

Thank you for your time and consideration.

Regards,
Jakub