SOURCE

var canvas = document.getElementById('canvas'),
ctx = canvas.getContext('2d'),
w = canvas.width = window.innerWidth,
h = canvas.height = window.innerHeight,

hue = 217,
stars = [],
count = 0,
maxStars = 1100;                //星星数量,默认1300
var canvas2 = document.createElement('canvas'),
ctx2 = canvas2.getContext('2d');
canvas2.width = 1000;
canvas2.height = 1000;
var half = canvas2.width / 2,
gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
gradient2.addColorStop(0.025, '#CCC');
gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
gradient2.addColorStop(1, 'transparent');

ctx2.fillStyle = gradient2;
ctx2.beginPath();
ctx2.arc(half, half, half, 0, Math.PI * 2);
ctx2.fill();

// End cache
function random(min, max) {
    if (arguments.length < 2) {
        max = min;
        min = 0;
    }

    if (min > max) {
        var hold = max;
        max = min;
        min = hold;
    }

    return Math.floor(Math.random() * (max - min + 1)) + min;
}

function maxOrbit(x, y) {
    var max = Math.max(x, y),
    diameter = Math.round(Math.sqrt(max * max + max * max));
    return diameter / 2;
    //星星移动范围，值越大范围越小，
}

var Star = function() {

    this.orbitRadius = random(maxOrbit(w, h));
    this.radius = random(60, this.orbitRadius) / 10;       //星星大小,值越大星星越小,默认8
    
    this.orbitX = w / 2;
    this.orbitY = h / 2;
    this.timePassed = random(0, maxStars);
    this.speed = random(this.orbitRadius) / 80000;        //星星移动速度,值越大越慢,默认5W
    
    this.alpha = random(2, 10) / 10;

    count++;
    stars[count] = this;
}

Star.prototype.draw = function() {
    var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
    y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
    twinkle = random(10);

    if (twinkle === 1 && this.alpha > 0) {
        this.alpha -= 0.05;
    } else if (twinkle === 2 && this.alpha < 1) {
        this.alpha += 0.05;
    }

    ctx.globalAlpha = this.alpha;
    ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
    this.timePassed += this.speed;
}

for (var i = 0; i < maxStars; i++) {
    new Star();
}

function animation() {
    ctx.globalCompositeOperation = 'source-over';
    ctx.globalAlpha = 0.5;                                 //尾巴
    ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
    ctx.fillRect(0, 0, w, h)

    ctx.globalCompositeOperation = 'lighter';
    for (var i = 1,
    l = stars.length; i < l; i++) {
        stars[i].draw();
    };

    window.requestAnimationFrame(animation);
}

animation();

//树
var treeCanvas = document.getElementById("treeAndFlower"),
        tCtx = treeCanvas.getContext('2d'),
        flowerCanvas = document.getElementById("animateFlower"),
        fCtx = flowerCanvas.getContext("2d"),
        cw = window.innerWidth,
        ch = window.innerHeight;
    treeCanvas.width = flowerCanvas.width = cw;
    treeCanvas.height = flowerCanvas.height = ch;
    var flowerList = [],
        rootTop = ch - 10,
        flowerColor = "rgba(255,192,203,.3)", //花色
        flowerColorDeep = "rgba(241,158,194,.5)", //花色深
        treeColor2 = "rgba(255,192,203,.5)", //树枝颜色
        treeColor = "#FFF", //树干颜色
        fallList = [], //飘落樱花列表
        g = 0.01, //重力加速度
        gWind = 0.005, //风力加速度
        limitSpeedY = 1, //Y速度上限
        limitSpeedX = 1; //X速度上限
    fCtx.shadowColor= "#FFF" ;
    fCtx.shadowBlur = 10 ;
    function drawTree(x, y, deg, step) {
      var addDeg = step % 2 === 0 ? 0.1 : -0.1,
          x1 = x + Math.cos(deg + addDeg) * (step + 4) * 0.8,
          y1 = y + Math.sin(deg + addDeg) * (step -1) * 0.8;
      tCtx.beginPath();
      tCtx.lineWidth = step / 3;
      tCtx.moveTo(x, y);
      tCtx.lineTo(x1, y1);
      tCtx.strokeStyle = step > 5 ? treeColor : treeColor2;
      tCtx.stroke();
      if (step > 20) {
        tCtx.fillStyle = treeColor;
        tCtx.arc(x, y, step / 6, 0, 2 * Math.PI);
        tCtx.fill();
      }
      if (step < 3 || (step < 23 && Math.random() > 0.1)) {
        var color = [flowerColorDeep, flowerColor][Math.round(Math.random() + 0.2)],
            r = 2 + Math.random() * 2;
        tCtx.fillStyle = color;
        tCtx.arc(x1 + Math.random() * 3, y1 + Math.random() * 3, r, 0, Math.PI);
        tCtx.fill();
        flowerList.push({
          x: x,
          y: y,
          sx: Math.random() - 0.5,
          sy: 0,
          color: color,
          r: r,
          deg: deg
        });
      }
      step --;
      
      if (step > 0) {
        drawTree(x1, y1, deg, step);
        if (step % 3 === 0) {
        
          drawTree(x1, y1, deg + 0.2 + Math.random() * 0.3, Math.round(step/1.13));
        }
        if (step % 3 === 1) {
             drawTree(x1, y1, deg - 0.2 - Math.random() * 0.3, Math.round(step/1.13)); 
        }
      
      }
       
      
    }
    function update() {
      if (Math.random() > 0.3) {
        fallList.push(flowerList[Math.floor(Math.random() * flowerList.length)]);
      }
      fCtx.clearRect(0, 0, cw, ch);
      for (var i=0; i<fallList.length; i++) {
        var fall = fallList[i];
        if (fall.sy < limitSpeedY) {
          fall.sy += g;
        }
        fall.sx += gWind;
        fall.x += fall.sx;
        fall.y += fall.sy;
        fall.deg += fall.sx * 0.05;
        if (fall.y > rootTop) {
          fallList.splice(i, 1);
          i --;
          continue;
        }
        fCtx.beginPath();
        fCtx.fillStyle = fall.color;
        fCtx.arc(fall.x, fall.y, fall.r, fall.deg, fall.deg + 1.3 * Math.PI);
        fCtx.fill();
      }
      requestAnimationFrame(update);
    }
   
      drawTree(cw / 2, rootTop, -Math.PI/2, 30);
 //执行
   update()

<body class="box">
  <canvas id="canvas"></canvas>
  <canvas id="treeAndFlower"></canvas>
  <canvas id="animateFlower"></canvas>
</body>

body{
  background-color: #161325;
  width:100%;
  height:100%;
}
canvas{
    position: absolute;
    left: 0;
    top: 0;
}