html - responsive svg polygon
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"
viewBox="0 0 1000 20" preserveAspectRatio="none" width="100%" height="20">
<polygon points="0,0 1000,0 500,20" style="fill:#cc3333; stroke: lightgrey; stroke-width: 6;"/>
</svg>