Hi retrocoal :-D
The game on itch.io is currently in 1000px / 750px.
Which means the visuals are at this resolution. These are not larger visuals that I would then scale down to CSS.
My game is in 4:3 for the old school look.
I don't think there is a perfect resolution. I made this choice for reasons of faster loading and display. But there are surely ways to manage the memories of his game that I do not know.