mobile-config-firefox/content/dark_settings_pages.css

/* Recolors addons manager, preferences page and new about:config */


@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
@namespace html url("http://www.w3.org/1999/xhtml");

@-moz-document url-prefix("about:addons"),
  url-prefix("about:preferences"),
  url-prefix("chrome://mozapps/content/extensions/aboutaddons.html"){
  :root,
  html|html{
    --in-content-page-color: rgb(210,210,210) !important;
    --in-content-text-color: rgb(210,210,210) !important;
    --in-content-page-background: rgb(46,54,69) !important;
    --in-content-box-background: rgba(255,255,255,0.1) !important;
    --in-content-deemphasized-text: var(--in-content-text-color) !important;
  }
  
  menulist > menupopup{ background-color: var(--in-content-page-background) !important; }
  
  .updateSettingCrossUserWarningContainer,
  .info-panel,
  .extension-controlled,
  .message-bar,
  html|message-bar,
  .alert,
  treecol{
    background-color: var(--in-content-box-background) !important;
    color: var(--in-content-text-color) !important;
  }
  .menulist-dropmarker,
  .checkbox-icon{
    -moz-context-properties: fill;
    fill : CurrentColor !important;
  }
}

/* Get addons page */
@-moz-document url-prefix("https://discovery.addons.mozilla.org/"){
  html|*{ color: inherit !important; }
  html|html,html|body{
    background-color: rgb(46,54,69) !important;
    color: rgb(210,210,210) !important;
  }
  html|div.addon,html|div.Notice{ background-color: rgba(255,255,255,0.1) !important; }
}

/* New about:config */
@-moz-document url-prefix("about:config"){
  html|html{
    --in-content-page-color: rgb(210,210,210) !important;
    --in-content-text-color: rgb(210,210,210) !important;
    --in-content-page-background: rgb(46,54,69) !important;
    --in-content-box-background: rgb(56,64,79) !important;
  }
}