In my opinion, HTML+CSS still remain quite inappropriate languages for describing desktop UIs. They can be used for such purposes, but, as compared with specialized languages (Glade XML, XAML, XUL), HTML+CSS is overly verbose for any non-trivial UIs, The worst thing is not code bloat and need for a Turing-complete language (JS) just to describe the looks, but the fact that you just can't have consistent system-wide look-and-feel. I believe, there's still completely no way to, say, bring proper system tabs or tree views to HTML+CSS+JS application.
It's interesting how the traditional definition of 'native look and feel' is starting to seem passé. Most of the computers I have sitting around the house today do not utilize a tree view in any default 'app'. There are no interface components on my tablet (that I can think of) that can't be recreated with some combination of HTML, CSS and JavaScript in a modern browser.
That's fair, but other than that, I'm curious what there is. CSS is still bad at grids without pretending they're tables, but Flexbox has solved most of the other limitations.
Keyboard acceleration. I have never seen an HTML control kit that handles the Tab or Arrow keys correctly or even very well.
No standards. For example - Drag and Drop. There is no standard system for Drag and Drop between components in the browser because it doesn't know about these controls, it only knows div div div div div. So, in general - it's just harder to write good code that targets HTML components because there are no standards for complex components.
(Some more patterns with no standards for complex components: Data Binding, Encapsulation (grouping one or more component into a parent component and walking parent/child components), Inheritance.)
And then, there's performance. Native trumps HTML here, no contest.
