From Melvor Idle

Template for embedding text in a spoiler box. Minimum syntax is {{SpoilerBox|text=internal text}} to get

The following content contains spoilers! Expand to view.
internal text

There are also arguments for title & color, for example {{SpoilerBox|text=internal text|title=title|color=green}} gives

internal text

The color argument also accepts 'default' as a special value, which causes the title text to remain as the default wiki text color. For example:

{{SpoilerBox|text=internal text|title=Default text color|color=default}} gives

Default text color
internal text