styles.css

/** Needed for [[Manual:Collapsible_elements/Demo/Advanced]] **/
#collapse-pre-one  .mw-collapsible-toggle .up,
#collapse-pre-one.mw-collapsed .mw-collapsible-toggle .down {
 display: none;
}
#collapse-pre-one .mw-collapsible-toggle .down,
#collapse-pre-one.mw-collapsed  .mw-collapsible-toggle .up {
 display: block;
}