This looks promising, and preferable to Mermaid. I did something similar in parallel with you! My version is here, which also allows per-diagram CSS to be specified: https://observablehq.com/@jwolondon/hello-pele

Nice, thank you for sharing. Yes, mount is probably preferable to render so that it can be responsive… The scoped styles are also nice. I prefer the tagged template literal, though. You could likely do the styles as pele.style(`.pele { … }`)`flowchart …`. We do something similar for tex.options; see https://github.com/observablehq/notebook-kit/blob/main/src/runtime/stdlib/tex.ts.