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

a.cp_btn {
	position: relative;
	display: block;
	width: 160px;
	padding: 0.8em;
	text-align: center;
	text-decoration: none;
	color: #fff;
	background: #2196F3;
	border:solid 1px #fff;
	overflow: hidden;
}
a.cp_btn:before {
	content:"";
	position: absolute;
	top: -25px;
	left: -20px;
	height:90px;
	width:20px;
	background : #fff;
	opacity: 0.3;
	transform: rotate(40deg);
	transition: 0.3s;
}
a.cp_btn:hover:before {
	left:98%;
}