Template:Hidden begin

Use the command

{{hidden begin|toggle=right|title=Title shown in hiding bar|titlestyle=background:#ccccff}}

before the thing that should be hidden, and the command

{{hidden end}}

afterwards.

You can read more at the Wikipedia page for this template: http://en.wikipedia.org/wiki/Template:Hidden_begin

Extra: In this wiki, the background of the hidden/shown box has a color. In order to have a transparent background, use

{{hidden begin|toggle=right|title=Title shown in hiding bar|titlestyle=background:#ccccff|bg2=transparent}}