Can MIXXX be considered professional software?

The skins are made using XML and QSS (Qt CSS).

It's not web per se, but it is not too far from it either. I would say it's a combination of both, Web and Desktop technologies, into one.

https://i0.wp.com/djtechtools.com/wp-content/uploads/2021/07...

It's not web technology by any stretch of imagination

What about a dense ui is intrinsically more difficult to implement on the web? Doesn't dense just mean lots of buttons/fields and small margins between them? Your example looks very challenging indeed, but it was probably not trivial to implement either way.

> What about a dense ui is intrinsically more difficult to implement on the web?

You have no control over layout or control over rendering. In native apps (especially desktop apps) you can always go down or up any level you want. In the browser you're always fighting the quite rigid and high-level layout and rendering engine.

It's somewhat better now with grid and felxbox, but the browser will always have its own ideas on how the children can be laid out, and there are no good ways for children to depend on the parent, or for the parent to depend on the children etc.

There are very, very few dense layouts on the web. And while late-90s/early-2000s sofware was often ridiculed, you could create dense control-rich interfaces in minutes. Because they are usually not ad-hoc hacks added to the platfrom as an afterthought, like everything on the web.