place item center

center.html

<div class="parent">
  <div class="child">
    1 line center
  </div>
</div>

style.css

.parent {
  display: grid;
  place-items: center;
  width: 100vw;
  height: 100vh;
  background: #a96da3;
}

.child {
  background: #fff;
  padding: 2em;
  border-radius: 20px;
  font-size: 1em;
  font-style: italic;
}