z-index not working with fixed positioning

Question

I have a div with default positioning (i.e. position:static) and a div with a fixed position.

If I set the z-index

Answer 1

Add position: relative; to #over

    #over {
      width: 600px;
      z-index: 10;
      position: relative;    
    }
    
    #under {
      position: fixed;
      top: 5px;
      width: 420px;
      left: 20px;
      border: 1px solid;
      height: 10%;
      background: #fff;
      z-index: 1;
    }

    
    
    
    	

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Fiddle