html 5 canvas 绘制太极demo

<div class="container">
<canvas id="myCanvas" width="400" height="400" ></canvas>
</div>

* {
padding: 0;
margin: 0;
}

body {
background-color: #d5d3d4;
}

.container {
width: 500px;
height: 500px;
position: relative;
top: 80px;
left: 50%;
transform: translateX(-50%);
background-color: #fff;
border-radius: 10px;
box-shadow: 0 0 5px #c2bfbf;
}
#myCanvas{
border:1px solid #000;
position:relative;
top: 50px;
left: 50px;
transform:translate(-50%,-50%);
border-radius:50%;
animation: myfirst 30s linear infinite;
}
@keyframes myfirst
{
0%   {transform:rotate(0deg);}
100% {transform:rotate(360deg);}
}

window.onload = function () {
var canvas=document.getElementById("myCanvas");
var ctx=canvas.getContext("2d");
ctx.beginPath();
ctx.arc(200, 100, 100, -0.5 * Math.PI, 0.5 * Math.PI, false);
ctx.arc(200, 300, 100, 1.5 * Math.PI, 0.5 * Math.PI, true);
ctx.arc(200, 200, 200, 0.5 * Math.PI, 1.5 * Math.PI, false);
ctx.closePath();
ctx.fillStyle = "black";
ctx.fill();

ctx.beginPath();
ctx.arc(200, 100, 25, 0 * Math.PI, 2 * Math.PI, false);
ctx.fillStyle = "white";
ctx.fill();
ctx.beginPath();
ctx.arc(200, 300, 25, 0 * Math.PI, 2 * Math.PI, false);
ctx.fillStyle = "black";
ctx.fill();
}