<!DOCTYPE HTML>
<style>
canvas {
    width: 40px;
    height: 40px;
    background: blue;
    position: absolute;
    top: 80px;
    left: 10px;
}
#background {
    width: 100px;
    height: 100px;
    background: green;
    position: absolute;
    transform: translateZ(0);
}
#overlap {
    width: 10px;
    height: 10px;
    background: grey;
    position: absolute;
    top: 20px;
}
</style>
<div id="background"></div>
<div id="overlap"></div>
<canvas></canvas>