Solved! Go to Solution.
    <viewer:WidgetTemplate id="wTemplate">
  <s:Rect bottom="0"
    left="0"
    right="0"
    top="0">
   <s:stroke>
    <mx:SolidColorStroke 
          alpha="{getStyle('borderAlpha')}"
          color="{getStyle('borderColor')}"
          weight="1"/>
   </s:stroke>
   <s:fill>
    <s:SolidColor alpha="1" color="0xffffff"/>
   </s:fill>
  </s:Rect>
  <esri:Legend id="myLegend"
                     width="100%" height="100%"
                     top="10"
                     respectCurrentMapScale="{respectCurrentMapScale}"/>
    </viewer:WidgetTemplate>
