html,body,svg { height:100%; margin:0; padding:0; }

by jpeter06

HTML

<!-- Learn about this code on MDN: https://developer.mozilla.org/en-US/docs/Web/SVG/Element/animate -->

<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <path d="M 0 0 l 0 50 l  50 0" fill="black" id="myPath"/>
    <animate attributeName="d" 
    values="M 0 0 l 0 30 l  30 0;M 0 0 l 0 50 l  50 0" dur="10s" repeatCount="indefinite" />
  </path>
</svg>

CSS

html,body,svg { height:100%; margin:0; padding:0; }