Other than to add a css rule for the toolbar to be: visibility: hidden;
, how can I hide the default viewer UI?
I saw this but I couldn't find what makes the bottom UI hidden.
You can use the "headless" viewer if you don't want any UI at all:
var viewer = new Viewer3D(domContainer)
But I don't see what's wrong with setting the css, it's a dom element, so any API you use would ultimately impact the css ...