Canvas collapses – Absolute Position / Overlay

Hi

I’ve created an overlay div and positioned the div absolutely over a hero section with css:

.overlay {
  display:block;
  position:absolute;
  top:30%;
  left:40%;
  z-index:10;
}

This works fine in inspector until you resize the window and canvas redraws from <canvas width="750" height="200"></canvas> to <canvas width="0" height="0"></canvas>.

How can I prevent canvas from collapsing?

Thanks