php-flarum/less/admin/MailPage.less

.MailPage {
  padding: 20px 0;

  @media @desktop-up {
    .container {
      max-width: 600px;
      margin: 0;
    }
  }

  fieldset {
    margin-bottom: 30px;

    > ul {
      list-style: none;
      margin: 0;
      padding: 0;
    }
  }
}

.MailPage-MailSettings-input {

  label {
    margin-bottom: 5px;
  }

  .FormControl {
    margin-bottom: 7px;
  }

  .Select {
    display: block;
  }

  :last-child {
    margin-bottom: 0;
  }
}