Try this code:

  .mh-top-header.mh-top-header--default,

  .mh-top-bar-user-panel__user-info {

  font-size: 16px!important;

  line-height: 44px!important;

  height: auto!important;

  }
  .mh-top-header .mh-top-bar-user-panel__main-link:before {

  top: 12px!important;

  }

In this article you can find information how to add custom CSS to any WordPress Theme: How to add CSS code that is future update compatible