discourse-calendar/assets/stylesheets/mobile/discourse-post-event-core-ext.scss

.raw-topic-link {
  .event-date-container {
    display: block;
    margin-top: 0.25em;

    .event-date {
      margin: 0;
    }
  }
}

.header-title {
  .event-date {
    display: none;
  }
}