Yes, on retina plain SqueakJS uses half the resolution, and by default the canvas interpolates. It looks sharper if you force pixel doubling: https://squeak.js.org/run/#url=https://freudenbergs.de/bert/... (by appending the pixelated flag to the url) but this looks worse when scaled, e.g. on iPad, so it's not the default. Caffeine, however, does support an HTML canvas - just try the included example which opens a workspace in HTML.
Someone broke that page (it's a Lively page, meaning it's editable by anyone). Here is a stand-alone version, running ThingLab: http://www.cdglabs.org/thinglab/
You first extend the environment with tests, then add the code to make them green. All without ever having to restart the "program".