html,body,svg { height:100% }

by Nidnogg

HTML

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

<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <!-- Example of a polygon with the default fill -->
  <polygon points="20,100 50,25 50,75 100,0" />

  <!-- Example of the same polygon shape with stroke and no fill -->
  <polygon points="100,100 150,25 150,75 200,0"
            fill="none" stroke="black" />
</svg>

CSS

html,body,svg { height:100% }