Custom menu with dropdowns

When a top-level menu entry has children but none of those children have children themselves, the theme renders it as a dropdown toggle button in the navigation bar.

The navigation above is driven by the demo_dropdown menu defined in menus.en.toml and activated on this page with:

main_menu: "demo_dropdown"
[[demo_dropdown]]
    name = "Home"
    url = "/"
    weight = 1

[[demo_dropdown]]
    identifier = "demo-dropdown-docs"
    name = "Docs"
    url = "#"
    weight = 2

[[demo_dropdown]]
    parent = "demo-dropdown-docs"
    name = "Components"
    url = "/components/"
    weight = 1

[[demo_dropdown]]
    parent = "demo-dropdown-docs"
    name = "Front Matter"
    url = "/frontmatter/"
    weight = 2

[[demo_dropdown]]
    parent = "demo-dropdown-docs"
    name = "Configuration"
    url = "/configuration/"
    weight = 3