fenix-fox/chrome/autohide_main_toolbar.css

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/autohide_main_toolbar.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* This style hides the main toolbar and shows it when the cursor is over the tabs toolbar (but not bookmarks toolbar) as well as whenever the focus is inside nav-bar, such as when urlbar is focused. */

:root{ --uc-navbar-transform: -40px }
:root[uidensity="compact"]{ --uc-navbar-transform: -34px }

:root[sessionrestored] :where(#nav-bar,#PersonalToolbar){
  transform: translateY(var(--uc-navbar-transform))
}
#nav-bar{
  opacity: 0;
  transition: opacity 200ms ease 1.8s, transform 400ms ease 1.8s !important;
  position: relative;
  z-index: 2;
}

#titlebar{ position: relative; z-index: 3 }

#navigator-toolbox:focus-within > .browser-toolbar,
#titlebar:hover ~ .browser-toolbar,
#nav-bar:hover,
#nav-bar:hover + #PersonalToolbar{
  transform: translateY(0);
  opacity: 1;
  transition-duration: 500ms !important;
  transition-delay: 0s !important;
}
#PersonalToolbar{ transition: transform 400ms ease 1.8s !important; position: relative; z-index: 1 }
:root[sessionrestored] > body > #browser{ margin-top: var(--uc-navbar-transform); }