Dropdown Markers and Animation
:chevron: chooses which arrow marks the open/closed state. The value names
the pair of directions the marker moves between, and only the closed half is
drawn — the stylesheet rotates it on open.
right-down (the default)
The marker points right when closed and down when open. Writing no
:chevron: at all gives the same result.
down-up
The marker points down when closed and up when open.
:animate: reveals the body with a transition instead of an instant jump.
fade-in
The body fades in.