> orthogonal to reasons

That's my impression too. I suspect that those "gray boxes" talks (a.k.a. buttons a la turrets of Panzerkampfwagen VI Tiger) are orthogonal to GUI in general.

Yet "memory and CPU usage" is also orthogonal to HTML/CSS per se. One of strict requirements of AntiVirus applications is to to consume as low memory and CPU as possible. And most of AVs are using HTML/CSS UI these days. And so Sciter code works on 600 mln PCs and Macs as a part of these applications.

In fact the main motivator why Sciter started using GPU for UI rendering was R&D director of Norton Antivirus when high-res monitors started to arrive. Retina monitors have 9 times more pixels to rasterize than old 96 ppi monitors. GPU is the only option for the GUI at post-Moore era.