<a href="#" class="cp_btn">button</a>

a.cp_btn {
	display: block;
	position: relative;
	width: 160px;
	padding: 0.8em;
	text-align: center;
	text-decoration: none;
	color: #fff;
	border:1px solid #8BC34A;
	background: #8BC34A;
	overflow: hidden;
	z-index: 1 !important;
}
a.cp_btn:after {
	content:"";
	position: absolute;
	top: 50%;
	left: 50%;
	height: 0;
	width: 100%;
	background : #fff;
	opacity: 0;
	transform: translateX(-50%) translateY(-50%) rotate(45deg);
	transition: 0.3s;
	z-index: -1;
}
a.cp_btn:hover {
	color: #da3c41;
}
a.cp_btn:hover:after {
	height: 250%;
	opacity: 1;
}
a.cp_btn:active:after {
	height: 350%;
	opacity: 1;
}