discourse/app/assets/stylesheets/common/select-kit/topic-notifications-button.scss

.topic-notifications-button {
  &.is-loading {
    pointer-events: none;
    user-select: none;

    .d-icon-spinner {
      margin: 0;
    }

    .selected-name .d-icon {
      display: none;
    }

    .topic-notifications-options {
      opacity: 0.5;
    }
  }
}