> I've always wanted to build a direct-browser integration that could use HTML+CSS for the layout, but avoids needing a JS runtime. Idk how lightweight servo is but one day I hope I will see my idea come to light

Blitz (https://github.com/DioxusLabs/blitz) is exactly that. It's a new custom browser engine supporting standard HTML/CSS with a native Rust API (and optional integration with Dioxus which is a React-like UI framework in Rust). Baseline binary sizes are around 10mb.

We share a few components with Servo (Stylo the CSS engine (also shared with Firefox), and html5ever the HTML parser), but we've built a bunch ourselves too: notably we have our own layout engine, DOM tree and event handling. Servo is unfortunately tightly coupled with SpiderMonkey, and there is little prospect of removing that dependency in the short term.