Both screen size toggles.
When playing Club Penguin, there was a feature at the top called the Screen Size Toggle. It makes the screen bigger or smaller. This was one of the features added from the Club Penguin Improvement Project. When the feature was added, if you toggled between big and small screen you would automatically be logged off. In 2012, a feature was added to the screen size toggle allowing you to change between big and small screen without being logged out. It was eventually removed in January 2015.
Purpose
The feature was added to reduce lag for players with a slower connection to Club Penguin for more pleasant gameplay, because by reducing the size of the screen, the less resolution the screen needs to render.