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

#topic-footer-buttons {
  .topic-notifications-button {
    min-width: auto;
    margin: 10px 0 15px 0;

    .btn {
      margin: 0;
    }

    .reason {
      line-height: 16px;
      margin: 0 0 0 10px;

      a {
        margin-left: 3px;
        margin-right: 3px;
      }
    }
  }
}

.topic-notifications-button .topic-notifications-options {
  min-width: auto;
}

.topic-notifications-button {
  display: inline-flex;
  justify-content: flex-start;
  align-items: center;
  margin: 0;

  .topic-notifications-options, .reason {
    display: inline-flex;
  }
}