title: How can I align an element to be in center of and above another element in relative layout?
body: <p>Here's a picture so you can understand what I want:</p>
  
  <p><img src="https://i.stack.imgur.com/YwiGh.png" alt="enter image description here"></p>
  
  <p>I have this green element already set up in my relative layout, and what I want is to put another element (the black one in the pic) above it so it gets centered exactly in the middle of the green element.</p>
  
  <p>Keep in mind that the black element doesn't have a constant width, and it's bigger in width than the green one. </p>
  
  <p>There are stuff like android:layout_alignLeft and android:layout_alignRight which would be helpful if I wanted it aligned left or right, but as far as I know there is no android:layout_alignCenter so I don't know how to do this thing...</p>