mobile-config-firefox/chrome/compact_proton.css

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

/* Small changes to make proton roughly as compact as the old compact mode */

:root{
  --toolbarbutton-inner-padding: 6px !important;
  --proton-tab-block-margin: 2px !important;
  --tabs-shadow-size: 0px !important;
	--arrowpanel-menuitem-padding: 5px !important;
}

menupopup > menuitem,
menupopup > menu{ padding-block: 0.3em !important; }

#urlbar-container{ padding-block: 3px !important; }
/* This is kinda weird, but it makes the horizontal line between tabs and nav-bar render "inside" nav-bar thus tabs are more visibily separated even if there is less space there */
#nav-bar{ 
  box-shadow: inset 0 var(--tabs-shadow-size) 0 var(--tabs-border-color) !important;
}