Very nice idea/design. I have to ask :) Are you using a custom layout algo for drawing the nodes labels in the directed graph?
Looks like fixed spacing along x and letting the cards float along y which is very effective.
I have sometimes wondered why there isn't more convergence for a standard set of primitives/libraries/template engines for drawing graphs on the web.
graphviz .dot files would seem to be a natural DSL and then there are packages like dagre/mermaid but italways seems like for applications you need to end up rolling your own.