<style>
.genel_div { top: 0px; bottom: 0px; left: 0px; position: fixed; }
.whatsapp { margin: 0; position: absolute; top: 50%; -ms-transform: translateY(-50%); transform: translateY(-50%); }
</style>

<div class="genel_div">
<div class="whatsapp">
whatsapp
</div>
</div>