You can change the styling of the pagingbar in the lib .css.
To add a red border e.g., change the lib.css to (or overwrite in you theme css or custom css)
.mx-grid .mx-grid-controlbar .mx-grid-pagingbar {
  /* Buttons */
  /* Text Paging .. to .. to .. */
      border-style: solid;
    border-color: red;
}