.catalog-product-view #product-addtocart-button {
    float: left;
}

.buynow-button {
    margin-right: 1%;
    width: 49%;
    line-height: 3.6rem;
    font-size: 1.8rem !important;
}

@media screen and (max-width: 768px){
    .buynow-button{
        width: 100%;
    }
}