<div class="flag pink-triangle" role="img" aria-label="Pink Triangle Flag. An inverted pink triangle over a black background."></div>

.flag {
  width: 80vmin;
  aspect-ratio: 70 / 45;
}

.pink-triangle {
  background:
    conic-gradient(from 330deg at 50% 100%, #f7a 60deg, #0000 0) 50% 50% / 55% 73% no-repeat,
    black;
}