<div>CSS</div>

div {
  
  /* Define width */
  --width: 256px;

  /* Set width */
  width: var(--width);

  /* height = width */
  aspect-ratio: 1 / 1;

  /* Squircle, use Water Gun! */
  corner-shape: squircle;

  /* I found this formula on Reddit */
  border-radius: calc((var(--width) / 2) * 44.53125);
  
}

/* Ignore */

div {
  display: flex;
  place-items: center;
  justify-content: center;
  color: white;
  font: 900 5rem system-ui;
  background: linear-gradient(130deg, #ff7a18 0%, #af002d 41.07%, #319197 76.05%);
}