mobile-config-firefox/chrome/classic_firefox_menu_button.css

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

/* Makes the main menu button appear in the top left corner styled similarly to Firefox versions 4 to 29 */

#PanelUI-button{
   /* Nightly colors scheme */
  /*--uc-fx-button-color: #9752fa;
  --uc-fx-button-sec-color: #00b2fa8a;*/
   
  /* Release color scheme*/
  --uc-fx-button-color: #ff8313;
  --uc-fx-button-sec-color: #ffdfbf85;
}

#PanelUI-button{ -moz-box-ordinal-group: 0; margin-inline: 2px var(--uc-window-drag-space-pre,24px) !important; }
:root[tabsintitlebar] #nav-bar{ border-left-width: 0px; padding-left: 0px !important; }
#PanelUI-menu-button{ -moz-box-align: start !important; }
#PanelUI-menu-button > stack{
  background-color: var(--uc-fx-button-color);
  background-image: linear-gradient(var(--uc-fx-button-sec-color), transparent) !important;
  list-style-image: url(chrome://global/skin/icons/arrow-down-12.svg) !important;
  border-radius: 0 0 4px 4px !important;
  border: 2px groove var(--uc-fx-button-color);
  border-top: none;
  display: -moz-box;
  padding: 4px 10px !important;
}

#PanelUI-menu-button:hover > stack,
#PanelUI-menu-button[open] > stack{
  background-color: var(--uc-fx-button-color) !important;
  background-image: linear-gradient(rgba(100,100,150,0.3), transparent) !important;
}

#PanelUI-menu-button > stack::before{
  display: -moz-box;
  content: "Firefox"; /* Change text here */
  font-weight: 700;
  margin-inline-end: 4px;
}

/* OPTIONAL - move the menu button to top-left corner of the window.
 * Don't use this if you also use tabs_on_bottom.css
 */

/*
#PanelUI-button{
  position: fixed;
  display: flex;
  top: 0;
}

#toolbar-menubar,
#toolbar-menubar[autohide="true"] + #TabsToolbar{
  padding-left: 94px !important;
}

*/