<a class="btn btn-5">Hover</a>

*{
 box-sizing: inherit;
 transition-property: all;
 transition-duration: .3s;
 transition-timing-function: ease;
}

a {
 text-decoration: none;
}

.btn {
 color: #fff;
 cursor: pointer;
 display: block;
 font-size: 16px;
 font-weight: 400;
 line-height: 45px;
 margin: 0 auto;
 max-width: 155px;
 width: 100%;
 height: 45px;
 text-align: center;
 position: relative;
 text-transform: uppercase;
}

.btn-5 {
 border: 1px solid;
 overflow: hidden;
 position: relative;
}

.btn-5 span {
 z-index: 20;
}

.btn-5:after {
 background: #fff;
 content: "";
 height: 155px;
 left: -1px;
 opacity: .2;
 position: absolute;
 top: -50px;
 -webkit-transform: rotate(0deg);
 transform: rotate(0deg);
 transition: all 210ms ease-in-out;
 width: 85px;
 z-index: -10;
}

.btn-5:hover:after {
 left: 50%;
 transition: all 210ms ease-in-out;
}