<div
     class="parent"
     style="background: blue; width: 500px; height: 250px;"
     >
    <div
         class="child"
         style="color: white;"
         >
      I'm center with position
    </div>
</div>

/* Using positions */

.parent {
    position: relative;
}
.child {
    position: absolute;
    transform: translate(-50%, -50%);
    left: 50%;
    top: 50%;
}