I can't see any tools. could anyone tell me how to undo it?

[김지은]

I accidentally pressed some button, and tools like timeline and brushes don't come back. could anyone tell me how I can undo it? plz 

[DarrenT]

You've pressed the single backquote button (to the left of the number 1 on UK & USA keyboards). You can either press the button again or double click on the title bar of the viewer window (where it says Scene Untitled19). Double clicking on the title bar of any docked window in OpenToonz makes it full screen.