/* @license GPL-2.0-or-later https://www.drupal.org/licensing/faq */
.header__mega-menu li{line-height:1.1;margin-bottom:0.7rem;}.revamp-footnotes-item p{font-weight:400;font-family:Foundry Sterling Medium,Arial,Helvetica,宋体,SimSun,Nimbus Sans L,sans-serif;}
.container{height:200px;position:relative;border:3px solid green;}.vertical-center{margin:0;position:absolute;top:50%;-ms-transform:translateY(-50%);transform:translateY(-50%);}<div class="container">
  <div class="vertical-center">
    <button>Centered Button</button>
  </div>
</div>