Make an original one-button browser game in a single self-contained index.html with a <canvas> (640x300) and plain JavaScript, no libraries.
Mechanic: gravity flip. The player is a square on a floor (y=250) or a ceiling (y=50). Pressing Space, clicking or tapping flips gravity; the square accelerates toward the other surface (acceleration ~0.9 px/frame², max speed 12).
Obstacles: red rectangles 24px wide, 26–60px tall, attached to either the floor or the ceiling at random, scrolling left. Spawn gap shrinks as speed rises (start 4 px/frame, +1 every 600 frames).
Score = frames survived / 6. Game over on overlap; tap to restart. Save the best score in localStorage.
Draw everything with simple shapes. Use your own name and art. Show clear Start, Pause/Resume and Restart buttons. Run physics at a fixed 60 updates per second, independent of screen refresh rate. Pause when the tab is hidden and require Resume. Support touch and keyboard without repeated flips when a key is held. Best-score storage is optional and must not break the game if unavailable.