Property:
shadowOffsetY:

Canvas:
your browser does not support the canvas tag
Code:
var c=document.getElementById('myCanvas');
var ctx=c.getContext('2d');
ctx.shadowBlur=10;
ctx.shadowOffsetY=20;
ctx.shadowColor='black';
ctx.fillStyle='red';
ctx.fillRect(20,20,100,80);
Click the property values above to see the result
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