mask

html,
body,
svg {
  height: 100%;
}

<svg viewBox="0 0 200 100" xmlns="http://www.w3.org/2000/svg">
  <mask id="myMask" maskContentUnits="objectBoundingBox">
    <rect fill="white" x="0" y="0" width="100%" height="100%" />
    <polygon
      fill="black"
      points="0.5,0.2 0.68,0.74 0.21,0.41 0.79,0.41 0.32,0.74" />
  </mask>

  <!--
  Punch a hole in a shape of a star inside the red circle,
  revealing the yellow circle underneath
  -->
  <circle cx="50" cy="50" r="20" fill="yellow" />
  <circle cx="50" cy="50" r="45" fill="red" mask="url(#myMask)" />
</svg>