Centering Percentage Width/Height Elements

Centering

 body {
    background: #900;
    }
   
.box {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    width: 70%;
    height: 80%;
    padding: 20px;
    background: red;
    color: white;
    text-align: center;
    box-shadow: 0 0 30px rgba(0, 0, 0, 0.2);
    }

<div class="box">
    Percentage sized and still centered.
    </div>