The following example shows how you can change the up arrow and down arrow skins on a horizontal/vertical scroll bar in a Flex container by setting the horizontalScrollBarStyleName, verticalScrollBarStyleName, downArrowSkin, and upArrowSkin styles.

Full code after the jump.

View MXML

       layout="vertical"
       verticalAlign="middle"
       backgroundColor="white">

   
       Container {
           verticalScrollBarStyleName: myVScrollBarStyleName;
           horizontalScrollBarStyleName: myHScrollBarStyleName;
       }

       .myVScrollBarStyleName {
           downArrowSkin: Embed("assets/bullet_add.png");
           upArrowSkin: Embed("assets/bullet_delete.png");
       }

       .myHScrollBarStyleName {
           downArrowSkin: Embed("assets/bullet_add.png");
           upArrowSkin: Embed("assets/bullet_delete.png");
       }
   

   

              backgroundColor="haloSilver"
           horizontalScrollPolicy="on"
           verticalScrollPolicy="on"
           width="320"
           height="240">