title: Overlay panel (above another)
body: <p>I am learning how to use Swing and found myself quite difficult task.</p>
  
  <p>What I am trying to accomplish: I want to have panel (call it menu panel) on the left side (let's say 100px width) and the second panel (call it content panel), which takes the rest of available place.</p>
  
  <p>In menu panel there are 3 buttons. When I press on of them, to the right side of menu panel (over content panel) second menu panel (submenu) should appear (and it should start in the middle of button which was pressed).</p>
  
  <p>It may be hard to understand, so I've created simple draft:</p>
  
  <p><img src="https://i.stack.imgur.com/tsMdW.png" alt="enter image description here"></p>
  
  <p>I tried JLayeredPane but there were problems with resizing window (elements in Layered Pane didn't resize).</p>