Screen centering block

Based on table

HTML

<div class="full container fixed">
  <div class="row">
    <div class="modal">
      <h1>
       Here!
      </h1>
      <div>
        Is contenent here!
      </div>
    </div>
  </div>
</div>

CSS

.full { width:100%; height:100%;}
    .fixed { position: fixed; }
.container { display: table;  text-align: center; vertical-align:center; border:1px solid red; }
      .row { display: table-cell; line-height:100vh; }
    .modal { display: inline-block; line-height:1em; border:1px solid green; }