Both Android (ConstraintLayout) and iOS (Auto Layout) use Cassowary. Why not just implement this with CSS as well so we can use the same layout tech for every platform?
I totally feel you, and that is what Houdini’s Custom Layout is going to be about: https://github.com/w3c/css-houdini-drafts/blob/2b730220b2f3c...
I want to write a blog post about constraing based layouts on the web specifically, but the TL;DR on why we don’t have it already:
Standardization is hard. It’s especially hard to reach consensus when:
* the runtime for a layout algorithm is hard to estimate
* it can _fail_ (which is unprecedented in CSS)
* a new syntax for constrains would have to be defined.