HTML UI at the end is just a set of few simple concepts (at least with Sciter):

1. UI is a composition of just two universal components: Element and Node (text, comment, etc).

2. UI is a single rooted tree of such blocks - DOM tree.

3. The tree can be styled by well known CSS means.

4. Events are delivered to particular UI elements using bubbling/sinking event propagation schema.

5. Any DOM Element may have so called behavior assigned to it. The behavior is either native (C/C++/Rust/Go/etc) or script function. All <input> elements are normal DOM elements with corresponding behaviors attached.

I do not see how this simple setup can be an antithesis to anything.