/indra/newview/skins/default/xui/en/panel_volume_pulldown.xml

<?xml version="1.0" encoding="utf-8" standalone="yes" ?>
<panel
 background_opaque="true"
 background_visible="true"
 bg_opaque_image="Volume_Background" 
 bg_alpha_image="Volume_Background" 
 border_visible="false"
 border="false"
 chrome="true"
 follows="bottom"
 height="150"
 layout="topleft"
 name="volumepulldown_floater"
 width="32">
 <slider
  control_name="AudioLevelMaster"
  follows="left|top"
  left="0"
  top="1"
  orientation="vertical"
  height="120"
  increment="0.05"
  initial_value="0.5"
  layout="topleft"
  name="mastervolume"
  show_text="false"
  slider_label.halign="right"
  top_pad="2"
  volume="true">
  <slider.commit_callback
   function="Vol.setControlFalse"
   parameter="MuteAudio" />
  </slider>
  <button
    left="10"
    top_pad="9"
    width="12"
    height="12"
    follows="top|left"
    name="prefs_btn"
    image_unselected="Icon_Gear_Foreground"
    image_disabled="Icon_Gear_Background"
    image_pressed="Icon_Gear_Press"
    scale_image="false">
    <button.commit_callback
       function="Vol.GoAudioPrefs" />
  </button>
</panel>