I started a new job with a greenfield site in Angular to create a website from an old desktop app. I gave a presentation guided by my Supervisor who wants game style top icon menus to cut down on space usage, however it has now come to light that my supervisor wants the sites page's, width's and height's to be equal to the device resolution's width and height. I asked why and he replied that he wants a game style app. However the original app is granular in nature and one screen at its desktop would extend many screens on mobiles. Also to package the pages would be hellish and my experience is back end with bootstrap not front end, so my observations aren't being taken on board readily. He has some experience with writing gaming software but not websites. what can I say?
I recommend you create mockups of what the game would look like based on the requirements you've been given. Assuming that the mockups accurately illustrate what you've described in words, you can show them to your supervisor as a way of explaining that their design won't work well in all situations.
You could also give a good faith estimate of the amount of effort it would require to create the application to their specifications, and another with the amount of effort required to do it your way. Presumably the numbers would be wildly different based on what you wrote in your question. You need to be particularly diligent, however, and provide fair and reasonable estimates.
You need to remember that at the end of the day, you are creating his application, not yours. If you are not in a decision making role, then it is unfortunately not your decision to make. Once you've fulfilled your professional duties to explain the pros and cons of proposed solutions, it's up to the supervisor to make the final decision.