HTML and BODY are static, where’s my DIV closest positioned ancestor?

HTML

<div class="parent1">
      <div class="child1">I'm 25px height (50% of 50px)</div>
    </div>
    <div class="parent2">I'm absolute positioned. My ancestors, body and html, are static... Where I'm getting the 25% from?</div>

CSS

body { margin: 0; padding: 0; }
      .parent1 { height: 50px; background: #00ff00; }
      .parent1 > .child1 { height: 50%; width: 100%; background: #ffcc00; }
      .parent2 { position: absolute; width: 100%; height: 25%; background: #ff0000; }