They wouldn't be there if they didn't need to be there. Leave them alone, stop trying to break things.
I found out that components are children of this layer - above the canvas.
The "dom_overlay_container" ID is implemented as target in the code snippets for components behaviour.
So in most cases, the dom_overlay_container is empty and without function.
Yes, and it imposes an utterly insignificant storage overhead, so don't worry about it.
But it breaks my responsive design as it has fixed dimensions. So better remove it anyway.
You can use it for DOM animation, e.g.
Just paste this code in actions panel:
var div = document.getElementById('dom_overlay_container');
div.innerHTML += 'My Animated Text';
... and it is responsive just like the canvas.