.button-13 {
    width: 80px;
    height: 80px;
    border: none;
    border-bottom: solid 2px #c0c0c0;
    border-radius: 50%;
    box-shadow: inset 15px 30px 40px rgba(255, 255, 255, 0.5), 0 3px 7px rgba(0, 0, 0, .2);
    background-image: linear-gradient(#23e139 0%, #13d129 100%);
    color: #ffffff;
    font-weight: 600;
    font-size: 1em;
}