.filler {
    position: relative;
    padding-bottom: 100%;
    box-sizing: border-box;
}

.positioner {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  z-index: 0;

  & > *:first-child {
    inset: 0;
    flex: 1;
  }
}