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HTML 

              
                <canvas id="canvas" width="400" height="400"></canvas>
!

CSS 

              
                html {
  width: 100%;
  height: 100%;
}

body {
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #1C1D24;
  &:after {
    position: absolute;
    left: 50%;
    bottom: 1em;
    transform: translateX(-50%);
    content: 'Press arrow keys to start Snake';
    color: white;
    opacity: 0.4;
  }
}

canvas {
  border: 5px solid #272e38;
}
!

JS 

              
                var canvas, ctx;
      window.onload = function() {
        canvas = document.getElementById("canvas");
        ctx = canvas.getContext("2d");
        document.addEventListener("keydown", keyDownEvent);
        // render X times per second
        var x = 8;
        setInterval(draw, 1000 / x);
      };
      // game world
      var gridSize = (tileSize = 20); // 20 x 20 = 400
      var nextX = (nextY = 0);
      // snake
      var defaultTailSize = 3;
      var tailSize = defaultTailSize;
      var snakeTrail = [];
      var snakeX = (snakeY = 10);
      // apple
      var appleX = (appleY = 15);
      // draw
      function draw() {
        // move snake in next pos
        snakeX += nextX;
        snakeY += nextY;
        // snake over game world?
        if (snakeX < 0) {
          snakeX = gridSize - 1;
        }
        if (snakeX > gridSize - 1) {
          snakeX = 0;
        }
        if (snakeY < 0) {
          snakeY = gridSize - 1;
        }
        if (snakeY > gridSize - 1) {
          snakeY = 0;
        }
        //snake bite apple?
        if (snakeX == appleX && snakeY == appleY) {
          tailSize++;
          appleX = Math.floor(Math.random() * gridSize);
          appleY = Math.floor(Math.random() * gridSize);
        }
        //paint background
        ctx.fillStyle = "#1C1D24";
        ctx.fillRect(0, 0, canvas.width, canvas.height);
        // paint snake
        // Create gradient
      // Create gradient
      grd = ctx.createLinearGradient(0.000, 150.000, 300.000, 150.000);
      
      // Add colors
      grd.addColorStop(0.000, 'rgba(247, 149, 51, 1.000)');
      grd.addColorStop(0.151, 'rgba(243, 112, 85, 1.000)');
      grd.addColorStop(0.311, 'rgba(239, 78, 123, 1.000)');
      grd.addColorStop(0.462, 'rgba(161, 102, 171, 1.000)');
      grd.addColorStop(0.621, 'rgba(80, 115, 184, 1.000)');
      grd.addColorStop(0.748, 'rgba(16, 152, 173, 1.000)');
      grd.addColorStop(0.875, 'rgba(7, 179, 155, 1.000)');
      grd.addColorStop(1.000, 'rgba(111, 186, 130, 1.000)');
        ctx.fillStyle = grd;
        for (var i = 0; i < snakeTrail.length; i++) {
          ctx.fillRect(
            snakeTrail[i].x * tileSize,
            snakeTrail[i].y * tileSize,
            tileSize,
            tileSize
          );
          //snake bites it's tail?
          if (snakeTrail[i].x == snakeX && snakeTrail[i].y == snakeY) {
            tailSize = defaultTailSize;
          }
        }
        // paint apple
        ctx.fillStyle = grd;
        ctx.fillRect(appleX * tileSize, appleY * tileSize, tileSize, tileSize);
        //set snake trail
        snakeTrail.push({ x: snakeX, y: snakeY });
        while (snakeTrail.length > tailSize) {
          snakeTrail.shift();
        }
      }
      // input
      function keyDownEvent(e) {
        switch (e.keyCode) {
          case 37:
            nextX = -1;
            nextY = 0;
            break;
          case 38:
            nextX = 0;
            nextY = -1;
            break;
          case 39:
            nextX = 1;
            nextY = 0;
            break;
          case 40:
            nextX = 0;
            nextY = 1;
            break;
        }
      }
!
999px

Console