Screen Sizes - HUD - Button Layout - Camera.

Hello everyone. I hope you're all doing perfect!

Im here because I wanted help with understanding something with the camera view and the way button layout can be displayed.

So. I made a small idea of button layout for a menu but I'm having a hard time dealing with multiple screen sizes.

On my computer the layout seems pretty good but on a mobile device, such as an Optimus G device the buttons look really small and the positioning is different on my computer and the mobile(Im assuming this comes because I used percentage and not actual hardcoded numbers.)

So I wanted to ask everyone, do you have any recommendations/tips/advice on making a layout for multiple screens? (Plus the buttons look smaller on my mobile than on my computer...)(50px by 50px) :/

Thank you for your time and expertise. Have a good day