discourse/plugins/chat/assets/stylesheets/mobile/chat-message.scss

.mobile-view.has-full-page-chat {
  &.disable-message-actions-touch {
    .chat-message-actions {
      > * {
        pointer-events: none;
      }
    }
  }

  #skip-link {
    @include user-select(none);
  }

  #skip-link,
  .d-header,
  .chat-message-actions-mobile-outlet,
  .chat-channel,
  .chat-thread {
    > * {
      @include user-select(none);
    }
  }

  .chat-message-container {
    transition: transform 400ms;
    transform: scale(1);

    &.is-long-pressed {
      animation: scale-animation 400ms;
    }
  }

  @keyframes scale-animation {
    0% {
      transform: scale(1);
    }
    80% {
      transform: scale(0.95);
    }
    100% {
      transform: scale(1);
    }
  }
}