Source: bullet-threading.css

Use the cssclass bullet-threading to add a thread between bullet points in your lists when hovering them in preview (reading) view.

Hovering an item with a sublist will add a vertical thread next to all of its sublist.

---
cssclasses:
  - bullet-threading
---

- Solar bodies
    - Solar System
        - Terrestrial planet
        - Giant planet
            - Gas giant
            - Ice giant
        - Heliosphere
        - Oort cloud
            - Hills Cloud
        - Meteoroid
            - Micrometeoroid

CSS Variables

Same as for the tree-view.