<!DOCTYPE html>
<!--
 | Like "top", but specifies how far a box's bottom margin edge is offset
 | above the bottom of the box's containing block. For relatively positioned
 | boxes, the offset is with respect to the bottom edge of the box itself.
 |   https://www.w3.org/TR/CSS21/visuren.html#position-props
 -->
<html>
<head>
  <style>
    body {
      font-size: 100px;
    }
    div {
      height: 100px;
    }
    .containing-block {
      position: relative;
      height: 600px;
    }
    .green {
      color: green;
    }
    .blue {
      color: blue;
    }
    .absolutely-positioned {
      position: absolute;
      bottom: 300px;
    }
    .relatively-positioned {
      position: relative;
      bottom: -400px;
    }
  </style>
</head>
<body>
  <div class="containing-block">
    <div class="green relatively-positioned">world!</div>
    <div class="green">Hello,</div>
    <div><!-- Placeholder for "world!". --></div>

    <div class="blue absolutely-positioned">world!</div>
    <div class="blue">Hello,</div>
  </div>
</body>
</html>