session-desktop/stylesheets/_session_theme_dark.scss

// Messages
.dark-theme {
  .module-conversation-header {
    background-color: $session-color-dark-1;
  }
  .discussion-container {
    background-color: $session-color-dark-2;
  }

  .module-message__author {
    color: $session-color-dark-5;
  }

  .module-message__metadata__badge {
    color: $session-color-dark-4;
  }
  .module-message__metadata__date--incoming {
    color: $session-color-dark-4;
  }
  .module-message__metadata__date--outgoing {
    color: $session-color-dark-5;
  }

  .module-message__container--incoming {
    background-color: $session-color-dark-1;
  }

  .module-message__container--outgoing {
    background-color: $session-color-dark-3;
  }
}

.message-read-receipt-container {
  margin-left: 5px;
}