绘制一个带有黑色阴影的红色矩形

<canvas id="myCanvas" width="300" height="150" style="border:1px solid #d3d3d3;">

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</canvas>

<script>

  var c = document.getElementById("myCanvas");

  var ctx = c.getContext("2d");

  ctx.shadowBlur = 20;

  ctx.fillStyle = "red";

  ctx.shadowColor = "black";

  ctx.fillRect(20, 20, 100, 80);

  ctx.shadowColor = "blue";

  ctx.fillRect(140, 20, 100, 80);

</script>