session-desktop/stylesheets/_session_theme_dark.scss

// Messages
.dark-theme {
  .module-conversation-header {
    background-color: $session-shade-4;
  }
  .discussion-container {
    background-image: $session-gradient-black;
  }

  .module-conversation-header {
    border-bottom: none;
  }

  .module-message__author,
  .module-message__metadata__badge,
  .module-message__metadata__date--incoming,
  .module-message__metadata__date--outgoing {
    @include session-color-subtle($session-color-white);
  }

  .module-message__container--incoming {
    background-color: $session-shade-11;
  }

  .module-message__container--outgoing {
    background-color: $session-shade-5;
  }

  .module-message__container {
    transition: background-color 0.25s;
    box-shadow: 0px 0px 8px 2px rgba(0, 0, 0, 0.69);
  }
  .message-highlighted {
    background-color: $session-shade-5;
    border-radius: 0;
  }

  .message-selected {
    .module-message__container {
      background-image: $session-gradient-green;
      box-shadow: $session-dark-shadow;
    }

    .module-message__author {
      color: $session-color-white;
    }
  }
}

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