SVG绘制loading效果

<div class="loading">
        <svg width='40px' height='40px' xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" preserveAspectRatio="xMidYMid" class="uil-default">
        <rect x="0" y="0" width="100" height="100" fill="none" class="bk"></rect>
       <!--以一个点为原点，按一定角度旋转绘制矩形，并在矩形的opacity属性上添加上渐变效果 -->
        <!--rect绘制x y 是矩形左上角的坐标，width height是矩形的宽高，rx ry为矩形的圆角radius  rotate 旋转  -->
        <rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(0 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0s' repeatCount='indefinite'/></rect>
      <rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(30 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.08333333333333333s' repeatCount='indefinite'/></rect>
       <rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(60 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.16666666666666666s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(90 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.25s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(120 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.3333333333333333s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(150 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.4166666666666667s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(180 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.5s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(210 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.5833333333333334s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(240 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.6666666666666666s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(270 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.75s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(300 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.8333333333333334s' repeatCount='indefinite'/></rect><rect  x='46.5' y='40' width='7' height='20' rx='5' ry='5' fill='#00a9f2' transform='rotate(330 50 50) translate(0 -30)'>  <animate attributeName='opacity' from='1' to='0' dur='1s' begin='0.9166666666666666s' repeatCount='indefinite'/></rect>
       </svg>
    </div>