Edit in JSFiddle

<div class="wrap">
    <div class="vertical">aaaaa</div>
</div>

        body {
            background-color: #000;
        }
        .wrap {
            height: 500px;
            background-color: #fff;
        }
        .vertical {
            position: relative;
            top: 50%;
            transform: translateY(-50%);
        }