title: Change default popup menu submenu arrow
body: <p>I'm using default PopupMenu. I've customized it in my XML style, and now it has a dark style. but I have a problem now: please look at this screenShot I've prepared:</p>
  
  <p><a href="https://i.stack.imgur.com/ZKdGV.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ZKdGV.jpg" alt="enter image description here"></a></p>
  
  <p>As you can see the arrow is kind of hard to see and I really wish to avoid using popup window now. Is there any way that I could change it to a white arrow?</p>