Hey hey ~
Very impressed that you made this in html+css+javascript, game dev without an engine just adds a whole 'nother layer of time to things.
I wish that the timing for jumping was a little bit less tight, and for the player to have an little animation so it's less of a snapping movement.
I think it's really cool what you've accomplished here, and again hats off to you for doing this in html+css because that sounds like a nightmare. Well done :)