button {
	border-radius: 8px;
	}
.float{
	position:fixed;
	width:60px;
	height:60px;
	bottom:40px;
	right:40px;
	background-color:#25d366;
	color:#FFF;
	border-radius:50px;
	text-align:center;
  font-size:30px;
	box-shadow: 2px 2px 3px #999;
  z-index:100;
}

.my-float{
	margin-top:16px;
}

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css">
<a href="https://api.whatsapp.com/send?phone=212600240296&text=%D8%A7%D9%84%D8%B3%D9%84%D8%A7%D9%85%20%D8%B9%D9%84%D9%8A%D9%83%D9%85%20%D8%A3%D9%86%D8%A7%20%D9%85%D9%87%D8%AA%D9%85%20%D8%A8%D9%85%D9%86%D8%AA%D8%AC%D8%A7%D8%AA%D9%83%D9%85" class="float" target="_blank">
<i class="fa fa-whatsapp my-float"></i>
</a>