Why do QT applications display differently?

Question

Qt

I am running the PSI messenger on Ubuntu 18.04.2 LTS as a normal user and as a root user and I see a different display of windows (see screenshot). The size of the windows and the OK button are different. This applies to all QT applications I've tried, PSI is just an example. Please tell me who knows why this is happening and how to set it up so that the display is the same?
Thank you.

Answer 1

This applies not only to QT but also to GTK and depends on the theme settings of a particular user, and QT themes may differ from GTK themes.
Just take it as it is.

Answer 2

how to set it so that the display is the same?

https://packages.ubuntu.com/search?keywords=qt4-qt...
plus DE and font settings. they are user. Download the DE as root and see what it looks like.