how to create pop up that looks good for desktop and mobile?

Hello, I have a list of questions 🙂

1 – how do I create a pop up that looks good for BOTH desktop AND mobile?
When I try to make it look nice for desktop, it looks bad for mobile.
When I try to make it look nice for mobile, it looks bad for desktop.
Can I create 1 pop up design for mobile, and 1 pop up design for desktop?
It’s difficult to control the background image for mobile 🙁
What can I do?

2 – can I reset the template/layouts back to their original default settings (for colors, content etc)?
I have been messing around with the settings for so long, and now they look bad 🙁

Thank you very much,
~Kaiwin