@media (max-width: 768px) {
  .bx-im-message-content-text,
  .bx-im-message-content-text * {
    font-size: 18px !important;
    line-height: 1.45 !important;
  }

  textarea.bx-im-textarea-input {
    font-size: 18px !important;
    line-height: 1.45 !important;
  }
}