Canvas cutout
HTML
<canvas id="canvas" width="150" height="150"></canvas>JavaScript
var ctx = document.getElementById('canvas').getContext('2d');
ctx.fillStyle = 'rgba(0, 0, 0, 0.4)';
ctx.fillRect(0, 0, 150, 150);
ctx.translate(0, 0);
ctx.beginPath();
ctx.clearRect(10, 10, 50, 50);
ctx.clearRect(80, 20, 20, 50);
ctx.clip();