Just in case, I've published yesterday demo build of Sciter.JS that also has binaries for Raspberry Pi (ARM32).

See: https://github.com/c-smile/sciter-js-sdk (screenshots are there too)

Some stats:

Binary size : 3.7 Mb (RPI version)

HTML: HTML5 level of markup language + "HTML Window" extensions, see: https://sciter.com/html-window/

CSS 2.1 + selected modules of CSS3, see: https://sciter.com/docs/content/css/cssmap.html

JavaScript: full ES6 specification + extras like built-in JSX, see: https://github.com/c-smile/quickjspp

Again, Sciter.JS uses time proven and well known technologies in a fraction of size.