discourse/app/assets/stylesheets/common/base/personal-message.scss

.archetype-private_message {
  --border-radius: 2em;

  @keyframes current-user-background-fade-highlight {
    0% {
      background-color: var(--secondary);
      border-color: var(--primary-low);
    }
    100% {
      background-color: var(--tertiary-very-low);
      border-color: transparent;
    }
  }

  .topic-body .cooked {
    box-sizing: border-box;
    border: 1px solid var(--primary-low);
    margin-top: 0.25em;
    margin-left: -1.35em;
    padding: 1.5em 1.5em 0.5em 2em;
    border-radius: 0 var(--border-radius) var(--border-radius)
      var(--border-radius);
  }

  .current-user-post {
    &:not(.moderator) {
      .topic-body .cooked {
        background: var(--tertiary-very-low);
      }
      .topic-body.highlighted {
        @media (prefers-reduced-motion: no-preference) {
          .cooked {
            animation: current-user-background-fade-highlight 2.5s ease-out;
          }
        }
      }
    }
    .topic-body .cooked {
      border: 1px solid transparent;
    }
    .embedded-posts {
      .topic-body .cooked {
        border: 1px solid var(--primary-low);
        background: transparent;
      }
    }
  }

  .moderator {
    .topic-body .cooked {
      border: 1px solid transparent;
    }
  }

  .deleted .topic-body {
    .cooked {
      background: var(--danger-low);
    }
  }

  .whisper {
    .topic-body .cooked {
      background: transparent;
      border: 2px dashed var(--primary-low);
    }

    &.my-post .topic-body .cooked {
      border: 2px dashed var(--tertiary-very-low);
    }
  }

  .topic-avatar,
  .topic-body {
    border: none;
  }

  .post-menu-area {
    margin-top: 0.5em;
  }

  .post-notice {
    margin-bottom: 1em;
    border: none;
    background: var(--primary-very-low);
    border-radius: var(--border-radius);
    margin-left: 1.5em;
    box-sizing: border-box;
    padding: 1.5em 2em;
  }

  .topic-map {
    margin-left: -1.5em;
    border: none;
    border-radius: var(--border-radius);
    padding: 1.25em;

    section {
      border: none;
    }
    .map:not(.map-collapsed) {
      .avatars {
        margin: 0.5em 0;
      }
    }

    .participants {
      margin-bottom: 1.5em;
      .user {
        border: none;
        background: var(--primary-low);
        padding: 2px 4px;
        border-radius: var(--border-radius);
      }
    }
  }

  .map:first-of-type .buttons .btn {
    border: none;
    border-radius: var(--border-radius);
  }

  .embedded-posts {
    border: none;
    .topic-body {
      overflow: visible;
    }
    .topic-body,
    .topic-avatar {
      border: none !important; // overrides some specificity for .bottom
    }
    .collapse-down,
    .collapse-up {
      display: none;
    }
  }

  .timeline-replies {
    display: flex;
    align-items: baseline;
    margin-right: 0.15em;
  }

  .gap {
    margin-bottom: 2em;
  }
}