How to change system popup menu size

On Adwaita the system popup menu looks nice, but I prefer straight corners so I switched to Vimix theme, but the size is way smaller than expected. How can I change the popup size? Thanks.

what’s the application doing the pop-up ? You may be able to modify the config file of that application.

On i3, I use dunst. you can set all parameters in its config file dunstrc