mailinabox/management/templates/welcome.html

<style>
  .title {
    margin: 1em;
    text-align: center;
  }

  .subtitle {
    margin: 2em;
    text-align: center;
  }
</style>

<h1 class="title">{{hostname}}</h1>

<p class="subtitle">Welcome to your Mail-in-a-Box control panel.</p>