horse/resource/eui_skins/HScrollBarSkin.exml

<?xml version="1.0" encoding="utf-8"?>
<e:Skin class="skins.HScrollBarSkin" minWidth="20" minHeight="8" xmlns:e="http://ns.egret.com/eui">
    <e:Image id="thumb" source="roundthumb_png" scale9Grid="3,3,2,2" height="8" width="30" verticalCenter="0"/>
</e:Skin>