discourse/app/assets/stylesheets/mobile/modal-overrides.scss

.d-modal.discourse-local-dates-create-modal {
  .date-time-configuration {
    flex-direction: column;
    gap: 0.5em;
  }
  .calendar-date-time-input {
    width: 100%;
    margin: 0 0 1rem 0;
  }

  .picker-panel {
    //mysteriously needed to prevent it from overlapping the timezone-input
    position: relative;
    z-index: 0;
  }

  .pika-single {
    justify-content: center;
  }
}