@container (min-width: 200px) {
  #inner::before {} /* is #inner or #outer the container? */
  #inner::after {} /* is #inner or #outer the container? */
  #inner::first-letter {} /* is #inner or #outer the container? */
  #outer::first-letter {} /* is #inner, #outer, or an ancestor of #outer the container? */
  #inner::first-line {} /* is #inner or #outer the container? */
  #outer::first-line {} /* is #inner, #outer, or an ancestor of #outer the container? */
}