Okular doesn't follow dark theme of desktop. My eyes can't take white color, I tried to find a solution for it but it didn't work. Is there any way you know to make it follow dark theme?
What I tried: How to make Okular follow the system theme? - Ask Ubuntu
Problem about this solution was Qt5 app shut itself after selecting "gtk2".
Yep, Okular is a QT app.
Please see here;
I finally found a solution for this issue. I switched to Mint, didn't try this on Zorin but I believe it's also going to work on it.
Solution: https://www.reddit.com/r/linux/comments/psit31/flatpak_now_supports_qt_theming_with_kvantum/
Kvantum is very limited, providing support -only if there is a kvantum theme for it.
I tried it on Zorin... and immediately nuked it off my machine, never to be seen again.
I am sorry, I did not see your post from 28 days ago- or I was in a hurry and forgot it... But I have found a bug in Zorin OS since then that sets the QT_STYLE_OVERRIDE to gtk3 instead of gtk2. That file must be changed to gtk2 for the qt5ct settings to work.
No worries, thanks for your help. After I did this and restarted my pc, my panel's icons disappeared, but it didn't happen again after few tries. I wanted to update the post for helping others like me, white color hurts eyes a lot at night 
And day for me. 
I only use dark or at least semi-dark themes.
Light themes make me vampire-hiss.
