Some example custom CSS for Flarum

background-for-tag.less

.TagTile-info[href="/t/general"] {
  background-image: url(./custom/christmas-3015776_1920.jpg);
  background-size: cover;
  background-position: center center;
}

.DiscussionHero[style="background-color: rgb(136, 136, 136);"] {
  background-image: url(./custom/christmas-3015776_1920.jpg);
  background-size: cover;
  background-position: center center;
}

smaller-avatar.less

.PostUser-avatar {
  .Avatar--size(48px);
  left: -69px; // Original minus 16px
}

.PostUser-badges {
  width: 48px; // like avatar
  margin-left: -64px; // original plus 16 px
}

.Post {
  padding-left: 89px; // Original size minus 16 pixels, like the avatar
}

time-on-the-right.less

.Post-header > ul {
  display: flex;

  .item-meta {
    margin-left: auto;
  }
}