Build a complete, fully playable retro side-scrolling platformer website — an original-art homage to 1985-era plumber platformers (Super Mario Bros style), titled "SUPER PIXEL BROS." This is a real playable game, not a mockup: every mechanic below must actually work.

PAGES: One page only — the game IS the site. Dark "arcade cabinet" page, game canvas centered in a subtle CRT-style bezel, pixel-lettering title above, controls legend and "Built on IMD" credit below. All UI text in English.

TECH (strict): Single index.html with all CSS and JS inline. No frameworks, no CDN, no external images/audio/fonts, no build step; must work offline. Vanilla JS + Canvas 2D. Internal canvas 400×240 (16px tiles = 25×15 viewport), scaled to fit any window with letterboxing, image-rendering: pixelated. Fixed-timestep loop: physics at 60 Hz with accumulator, render on requestAnimationFrame. All sprites are ORIGINAL pixel art defined in code as palette-indexed string grids, pre-rendered to an offscreen atlas — do NOT embed or hotlink any copyrighted Nintendo graphics or any external asset. No per-frame allocations in the hot loop (pool fireballs/particles). Target 60 fps. Meta viewport, page title "Super Pixel Bros", inline data-URI favicon (pixel mushroom).

PLAYER & PHYSICS (start values, tune if it feels off): Small plumber with red cap, blue overalls, mustache; hitbox 12×16 small / 12×28 big. States: small → big (mushroom) → fire (flower); power-down one step with ~2s invincibility flash; hit while small = death animation (pop up, fall through floor, no input) then respawn. Walk accel 0.08 px/frame, run accel 0.12, ground friction 0.94, skid turnaround, walk max 1.5 px/f, run max 2.5. Variable-height jump: impulse −7.5; gravity 0.28 while jump held and rising, 0.5 otherwise; terminal fall speed 7; coyote time 4 frames; jump buffer 5 frames. Walk/run animation cycle, skid pose, jump pose, facing flips.

LEVELS & TILES: 3 complete levels, each 200+ tiles wide, defined in code as readable ASCII maps with a legend (# ground, B brick, ? question block, C coin, P pipe, = hard block, E enemy spawn, F flagpole...). Difficulty ramps; every level must be beatable. Level 1 sunny overworld (hills, bushes, clouds, pipes, pits, stair blocks). Level 2 sky/athletic with floating platforms, moving platforms, gaps. Level 3 underground palette (dark blue/black), tighter corridors, ceiling. Tiles: ground, brick (bump when small, break into 4 rotating fragments when big), ? block (coin or item, bump animation, becomes used block), spinning coins, green pipes of height 2-4, hard blocks, stair blocks; parallax background (clouds, hills, bushes drawn procedurally). Camera follows player horizontally with slight look-ahead, clamped to level bounds; vertical follow in level 2.

ENEMIES: Mushroom walker — walks and turns at walls, stomp = squash + 100 pts, side contact hurts player. Turtle — stomp = shell; kicking a still shell makes it slide, killing other enemies with combo scoring 100-200-400-800, and it hurts the player too; shell wakes up after ~6s. Piranha plant in at least 2 pipes (rises/lowers on a cycle, does not emerge while the player stands on that pipe). Enemies activate within ~1.5 screens of the camera, despawn far behind; pits kill them.

ITEMS & SCORING: ? blocks mostly give coins; the first ? block in each level gives a mushroom (or fire flower if already big); one hidden invisible 1-up block per level. Block coins pop up with animation; 100 coins = extra life. Fire state: shoot with run key, max 2 fireballs alive, they bounce along the ground, kill enemies, explode on walls. Level end: flagpole — grab height = bonus, slide down, auto-walk into the castle, "LEVEL CLEAR" banner with jingle, then next level. After level 3: "THANK YOU! YOU ARE A SUPER PLAYER!" win screen with final score and replay prompt.

HUD & SCREENS: Classic top HUD in pixel font: SCORE 000000, coin ×00, WORLD 1-1 to 1-3, TIME 400 counting down (time up = lose a life), LIVES ×3. Pit fall, time up, or enemy hit while small = lose a life; 0 lives = GAME OVER then title. Title screen with logo, "PRESS ENTER OR TAP TO START", high score saved in localStorage, and a controls overlay. Pause overlay (P/Esc), mute toggle (M) with visible icon.

AUDIO: All synthesized with WebAudio, initialized on first user gesture: jump, coin, stomp, bump, brick break, power-up, power-down, fireball, 1-up, death, flagpole, level-clear jingle; plus a short original chiptune background loop per level theme (square/triangle oscillators), quiet and pleasant, mutable with M.

CONTROLS: Keyboard — Arrow keys or A/D to move; Space/Z/W/Up to jump (hold = higher); X or Shift = run + shoot fireball; P/Esc pause; M mute; Enter start/confirm. Mobile — on-screen touch controls: left/right buttons bottom-left, B (run/fire) and A (jump) bottom-right; multi-touch must work so moving and jumping at the same time is possible; touch-action: none, no double-tap zoom, no long-press context menu, no text selection; canvas rescales correctly at 390×844 portrait and landscape.

ACCEPTANCE — TEST IN THE BROWSER BEFORE SHIPPING: (1) loads with zero console errors; (2) start, run right, stomp a walker, collect 5 coins (counter updates), hit a ? block, get the mushroom, grow, break a brick; (3) get the fire flower and kill an enemy with a fireball; (4) stomp a turtle, kick the shell, shell kills another enemy; (5) die once (pit or enemy) — life count drops and respawn works; finish level 1 — flag slide loads level 2; (6) pause and mute work; at mobile width the touch controls are playable and the frame rate feels smooth. Fix anything that fails before shipping; ship nothing placeholder. If any feature can't be done exactly as specified, ship a simpler but fully working version instead of a broken ambitious one.