mobile-config-firefox/chrome/autohide_bookmarks_and_main_toolbars.css

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

#navigator-toolbox{
  --uc-bm-height: 22px; /* Might need to adjust if the toolbar has other buttons */
  --uc-bm-padding: 2px; /* Vertical padding to be applied to bookmarks */
  --uc-navbar-height: -40px; /* navbar is main toolbar. Use negative value */
  --uc-autohide-toolbar-delay: 600ms; /* The toolbar is hidden after 0.6s */
}

:root[uidensity="compact"] #navigator-toolbox{ --uc-bm-padding: 1px; --uc-navbar-height: -32px }
:root[uidensity="touch"] #navigator-toolbox{ --uc-bm-padding: 6px }

@media (-moz-proton){
  #navigator-toolbox{
     --uc-bm-height: 26px; /* Might need to adjust if the toolbar has other buttons */
  }
  :root[uidensity="compact"] #navigator-toolbox{
    --uc-navbar-height: -34px;
    --uc-bm-height: 23px;
  }
}

:root[sessionrestored] #nav-bar,
:root[sessionrestored] #PersonalToolbar{
  background-image: var(--lwt-additional-images,var(--toolbar-bgimage)) !important;
  background-position: var(--lwt-background-alignment);
  background-position-y: calc(0px - var(--tab-min-height) - 2*var(--proton-tab-block-margin,0px));
  background-repeat: var(--lwt-background-tiling);
  transform: rotateX(90deg);
  transform-origin: top;
  transition: transform 135ms linear var(--uc-autohide-toolbar-delay) !important;
  z-index: 2;
}

:root[sessionrestored] #PersonalToolbar{
  background-position-y: calc(0px - var(--tab-min-height) - 2*var(--proton-tab-block-margin,0px) + var( --uc-navbar-height));
}

:root[lwtheme-image] #nav-bar,
:root[lwtheme-image] #PersonalToolbar{
  background-image: var(--lwt-header-image), var(--lwt-additional-images,var(--toolbar-bgimage)) !important;
}

#nav-bar[customizing],#PersonalToolbar[customizing]{ transform: none !important }

#navigator-toolbox > #PersonalToolbar{
  transform-origin: 0px var(--uc-navbar-height);
  z-index: 1;
  position: relative;
}

:root[sessionrestored]:not([customizing]) #navigator-toolbox{ margin-bottom:  calc(2px - var(--uc-bm-height) - 2 * var(--uc-bm-padding) + var(--uc-navbar-height)); }

#PlacesToolbarItems > .bookmark-item,
#OtherBookmarks,
#PersonalToolbar > #import-button{
  padding-block: var(--uc-bm-padding) !important;
}

/* Make sure the bookmarks toolbar is never collapsed even if it is disabled */
#PersonalToolbar[collapsed="true"]{
  min-height: initial !important;
  max-height: initial !important;
  visibility: hidden !important
}

/* The invisible toolbox will overlap sidebar so we'll work around that here */
#navigator-toolbox{ pointer-events: none; border-bottom: none !important; }
#PersonalToolbar{ border-bottom: 1px solid var(--chrome-content-separator-color) }
#navigator-toolbox > *{ pointer-events: auto }

#sidebar-box{ position: relative }

/* SELECT TOOLBAR BEHAVIOR */
/* Comment out or delete one of these to disable that behavior */

/* Show when urlbar is focused */
#nav-bar:focus-within + #PersonalToolbar,
#navigator-toolbox > #nav-bar:focus-within{
  transition-delay: 100ms !important;
  transform: rotateX(0);
}

/* Show when cursor is over the toolbar area */
#navigator-toolbox:hover > .browser-toolbar{
  transition-delay: 100ms !important;
  transform: rotateX(0);
}

/* Show when cursor is over popups/context-menus - cannot control which ones */
/*
#mainPopupSet:hover ~ box > toolbox > .browser-toolbar{
  transition-delay: 100ms !important;
  transform: rotateX(0);
}
*/

/* Uncomment to enable compatibility for multi-row_bookmarks.css */
/* This would break buttons placed in the toolbar but that is likely not happening if you are using multi-row setup  */
/*
#PersonalToolbar:not([customizing]){
  position: fixed;
  display: block;
  margin-bottom: 0px !important;
}
*/