This simple tutorial shows how to auto-hide the top bar in Ubuntu 18.04, Ubuntu 19.10 with the default Gnome desktop.
It’s easy to enable auto-hide the dock (left panel) feature as Ubuntu offers an option in the system settings utility. To run any maximized application window in full-screen like a video player does, you can also make the Gnome top bar auto-hide.
This can be done by a Gnome Shell extension called ‘Hide Top Bar’.
Open Ubuntu Software, search for and install
hide top bar gnome shell extension.
UPDATE: For Ubuntu 20.04, install the extension by pressing Ctrl+Alt+T to open terminal and run command:
sudo apt install gnome-shell-extension-autohidetopbar
Once installed, launch the extension settings either from Ubuntu Software in the install page, or by going to Gnome Tweaks -> Extensions.