.cp_btn {
    display: block;
    position: relative;
    width: 250px;
    padding: 0.8em;
    text-align: center;
    text-decoration: none;
    color: #fff;
    background: rgb(68, 148, 99);
    border:1px solid #fff;
    overflow: hidden;

    font-size: 16px;    
    font-weight: 600;

    outline: none;
}
.cp_btn:after {
    content:"";
    position: absolute;
    top: -100%;
    left: -100%;
    height: 100%;
    width: 275px;
    background : #fff;
    opacity: 0.3;
    transition: .4s;
}
.cp_btn:hover:after {
    top: 0;
    left: 0;
}