Frontend Mentor | Tip calculator app

I have tried to match my solution as best possible to the design. The challenge expects the user to hit the enter button to submit the form however I am not sure how to make that work on mobile devices or tablets. In order to make it work on mobile devices or tablets, I have added the button to submit the form for devices less than 500px. Do let me know if there are other ways to achieve this. Room for improvement is always there.

Many thanks. Happy coding