Press Ctrl + F11 / ⌘ F10 to hide Vivaldi Browser’s user interface.
You can hide the browser’s toolbars by enabling Full Screen view, but that maximizes the window and you’re not able to view the OS’ Task Bar or other open apps. As an alternative, you can just hide all toolbars and have the browser window as big or small as you want.
To quickly toggle Vivaldi’s user interface off and on, use the Keyboard Shortcut
Alternatively, use the following options: