Style not applied on mobile

Good day to everyone,
I am a newbie and I have managed to add some css to this page : databoy.space/iz40/ . You can see if you login: databoy.space/login/ . You can use username : [Removed by staff] and password: [Removed by staff] . The problem is on mobile phones the avatars are no longer round and the divs are no longer styled, But Why??