/* Completely hide tabs */
#TabsToolbar { visibility: collapse; }

/* hide navigation bar when it is not focused; use Ctrl+L to get focus */
#main-window:not([customizing]) #navigator-toolbox:not(:focus-within):not(:hover) {
  margin-top: -45px;
}
#navigator-toolbox {
  transition: 0.2s margin-top ease-out;
}