Imposter

.imposter {
  /* ↓ Choose the positioning element */
  position: var(--positioning, absolute);
  /* ↓ Position the top left corner in the center */
  inset-block-start: 50%;
  inset-inline-start: 50%;
  /* ↓ Reposition so the center of the element
is the center of the container */
  transform: translate(-50%, -50%);
}

.imposter.contain {
  /* ↓ Include a unit, or the calc function will be invalid */
  --margin: 0px;
  /* ↓ Provide scrollbars so content is not obscured */
  overflow: auto;
  /* ↓ Restrict the height and width, including optional
spacing/margin between the element and positioning container */
  max-inline-size: calc(100% - (var(--margin) * 2));
  max-block-size: calc(100% - (var(--margin) * 2));
}