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 {
    box-shadow: 0px 0px 8px 2px rgba(0, 0, 0, 0.69);
  }
  .module-message__container--incoming {
    background-color: $session-color-dark-1;
  }

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

  .message-highlighted {
    background-color: $session-color-dark-highlight;
    border-radius: 0;
  }
  .message-selected {
    background-color: rgba($session-color-dark-highlight, 0.8);
  }
}

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