Change the Skin of a Page
Steps
A page can use a skin of its own, which applies to that page and to every page nested under it, and wins over the wiki's. Skin Levels explains the order the settings are read in. You need administration rights on the page.
- Open the page the skin is for, then open its administration, as described in Administer a Page:

- Select the "Look & Feel" category, then its "Themes" section:

- Set the "Skin" field to one of the skins the wiki can use.
- Click "Save".
- Check that the "Skin" field holds the skin you chose. The page and every page nested under it are displayed with it from now on:

FAQ
Does a page nested in this one inherit the skin?
Yes. A page that sets no skin of its own is displayed with the skin of the closest page it is nested under that sets one, and with the wiki's if none of them does. Skin Levels gives the full order.
How do I make the page follow the wiki again?
Empty the "Skin" field and save. Empty is what the field holds until someone sets a skin, and it means the page inherits one instead of choosing it.
Why does the menu offer "Administer Parent" instead of "Administer Page"?
Because the page you opened is a terminal page, which carries no preferences of its own. The administration reached from it is the parent's, so a skin set there applies to the parent and to everything nested under it, not to the page you started from. Open the parent page itself to be sure of what the setting covers.