html {
  overflow: hidden;
  height: 100%;
  background: 
    linear-gradient(rgba(white, .64), rgba(white, .65)), 
    url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/2017/bg_slide_tiger_stretch.jpg);
  background-size: cover;
}

body { margin: 0; }

svg {
  display: block;
  margin: 0 auto;
  width: 100vmin; height: 100vmin;
}

.poly {
  fill: rgba(black, .32);
  stroke: crimson;
  stroke-miterlimit: 16;
  stroke-width: 15;
  vector-effect: non-scaling-stroke;
}