Sort of! On Windows, it's WebView2, which is more or less Chromium. On Mac it's the system's Safari, which I'm
pretty sure is frozen at the OS release (or maybe gets updated with OS updates). So I'm less worried that it'll break with an
update, but I've had to fix a few issues when someone is running on macOS 10.13 or something like that, where Safari is just missing some modern JS thing. I've solved that with polyfills and Babel and it's been alright.
CSS is the other issue, where old Safari doesn't support grid and some other stuff. So I stick to flexbox and well-supported stuff.