Some corners aren't rounded

I use Zorin 16.1 lite and when I was doing some customization I screwed up somewhere. pretty sure all corners are supposed to be rounded. in my case the upper corners are rounded and bottom ones aren't but in apps like nautilus file manager bottom corners are rounded as well

Do not worry that is normal, but is illogical and attracts occasional posts on the forum. Well I believe it is normal for Core (Gnome), but I see you are using Lite.
Others with Lite may wish to confirm this is indeed correct on xfce DE.

You could check your xfwm (windows manager) settings or try installing a new window theme such as this one to see if it changes anything: