前端页面漂亮的星空背景 ---js效果

html代码：

<div class="stars">div>

css代码

  html, body {
      height: 100%;
      overflow: hidden;
    }

    body {
      width: 100%;
      height:100%;
      background: #000;
      background-size: 100%;
      perspective: 500px;

    }
    .stars {
      position: absolute;
      top: 50%;
      left: 50%;
      width: 4px;
      height:4px;
      -webkit-border-radius:50%;
      -moz-border-radius:50%;
      border-radius:50%;
      animation: fly 2s linear infinite;
      transform-style: preserve-3d;
    }
    .stars:before, .stars:after {
      content: "";
      position: absolute;
      width: inherit;
      height: inherit;
      box-shadow: inherit;
    }
    .stars:before {
      transform: translateZ(-300px);
      opacity: .6;
    }
    .stars:after {
      transform: translateZ(-600px);
      opacity: .4;
    }

    @keyframes fly {
      from {
        transform: translateZ(0px);
        opacity: .6;
      }
      to {
        transform: translateZ(300px);
        opacity: 1;
      }
    }

js代码

    var w = document.documentElement.clientWidth*1.2;
    var h = document.documentElement.clientHeight*1.2;
    var star = document.getElementsByClassName("stars")[0];
    var n = 1000;
    //随机函数
    function randomNum(m, n) {
        return Math.floor(Math.random() * (n - m + 1) + m);
    }
    var str = '';
    for (var i = 0; i < n; i++) {
        var numX = randomNum(-w, w);
        var numY = randomNum(-h, h);
        var color = 'rgb(' + randomNum(0, 255) + ',' + randomNum(0, 255) + ',' + randomNum(0, 255) + ')';
        str += numX +'px'+' ' + numY+'px'+' '+ color+',';
    }
    str = str.slice(0,-1);
    star.style.boxShadow =  str;


            $(function(){

                  $('#main').fadeOut();

                  $('#main').fadeIn('slow');

        })