Use z-index of parent instead of hard-coding

[curlywurlycraig]

What is this?

This change uses the natural indexing rules of the browser by ordering canvas elements, rather than specifying a hard-coded z-index. This fixes issues relating to absolutely positioned canvases.

Context

I'm building a fun react-app that allows the moving around of little drawings on a kind of pin-board. Without this change, overlapping elements don't correctly obey the z-index of their parents, resulting in some weird visual issues:

But with this change, the CanvasDraw elements correctly obey their parents z-index:

[embiem]

Thanks for catching that & contributing!!

[curlywurlycraig]

You're welcome!