DIVS

HTML

<!-- WORKS -->
<canvas class="canvas1" id="canvas" width="400" height="400"></canvas>
<div class="divbox1">I'm a DIV</div>

<!-- DOESN'T WORK -->
<canvas class="canvas2" id="canvas" width="400" height="400"><div class="divbox2">I'm a DIV</div></canvas>

CSS

.canvas1,
.canvas2 {
    width:  200px;
    height: 200px;
    background-color: #F00;
    position: fixed;
    top: 10px;
    left: 10px;
}
.canvas2 {
    top: 240px;
}
.divbox1 {
    position: fixed;
    top: 10px;
    left: 10px;
    width: 100px;
    height: 100px;
    background-color: #00F;
}
.divbox2 {
    margin: 10px;
    background-color: #00F;
}