<!doctype html>
<meta charset=utf-8>
<style>
  div {
    position: relative;
  }
  svg {
    display: block;
    margin: auto;
  }
</style>
<body>
  <div>
    <svg xmlns='http://www.w3.org/2000/svg' width='100px' height='200px'
         viewport='0 0 100 200'>
      <rect x='0' y='100' width='100' height='100' fill='purple'>
      </rect>
    </svg>
  </div>
</body>