Autohide Top Panel is GNOME Shell Extension that lets you hide GNOME Shell top panel bar, Autohide Top Panel extension initially created by fpmurphy, this extension now available in GNOME Shell Extension website. See following video to see how it's works
Download Autohide Top Panel Extension
You can install Autohide Extension via GNOME Shell extension here, or download the extension through following links.
here, extract it and place it under /usr/share/gnome-shell/extensions (or ~/.local/share/gnome-shell/extensions).
After finished downloading, install extension using GNOME Tweak Tool then activate it by switch toggle on/off , once installed, refresh your desktop (log off the computer) to see it works.
|Activate Autohide Extension in GNOME Tweak Tool|