I was also a bit disappointed to find basic arithmetic. There is more. I was expecting something like an algorithm for a tile layout like https://masonry.desandro.com/ or https://github.com/d3/d3-hierarchy#treemap. In terms of animations, understanding linear algebra can help you take full advantage of CSS matrix and matrix3d transforms. Certain parallax effects can be done done better with trigonometry...
When you're implementing a user interface, you typically have some "design" or model of how it should work in your head. The main challenge is translating this intuitive model into a formal model that the computer can interpret for you. Math can definitely help you with this!
I think we should be emphasizing mathematical knowledge in front-end design and implementation, not trying to hide it under the covers. The better you are at math, the easier it is for you to implement the correct system for the design you want, and the less you have to compromise the design to fit the systems you have at hand.
How would one express those constraints? I think it's more efficient to let a human designer figure out some approximation of decent design and usability.
The way it's done in 2D sketch programs such as the sketch feature of Fusion 360 or Autodesk Inventor. Graphically. I've discussed this before on HN. All the modern CAD systems do this.
It took decades to get CAD GUIs right, but now they're quite good. They solve a far harder problem than web design. Look to them for guidance.
It's a completely different problem. CAD tools are modeling the physical world, so physical constraints make sense. UI designs often include completely non-physical dynamics that would be difficult to model using CAD-like constraints.
(Front end design ought to have more math behind the scenes, like a constraint solver, and less arithmetic visible to the web designer.)