<div class="ion-text-center my-class-parent">
        <ol class="my-class-child">
          <li>hi</li>
          <li>hi2</li>
        </ol>
    </div>

.my-class-parent {
  height: 100%;
  position: relative;
}

.my-class-child {
  position: absolute;
  left: 50%;
  top:30%;
  padding-left: 0;
}