CSS_woocommerce_button_round

a.button.product_type_simple.add_to_cart_button.ajax_add_to_cart {
    color: #fff;
    font-size: .85em;
    text-decoration: none;
    text-indent: -900em;
    text-align: center;
    width: 35px;
    height: 35px;
    display: block;
    z-index: 9500;
    box-shadow: none;
    text-shadow: none;
    margin: 0 auto!important;
    padding: 0;
    background-color: #66AD5F;
    border-radius: 100%;
}
a.button.product_type_simple.add_to_cart_button.ajax_add_to_cart:before,
a.button.product_type_simple.add_to_cart_button.ajax_add_to_cart:after {
    content: '';
    display: inline-block;
    border-top: 1px solid #fff;
    width: 16px;
    position: absolute;
    top: 17px;
    left: 9px;
    margin: 0;
    padding: 0;
    vertical-align: middle;
}
a.button.product_type_simple.add_to_cart_button.ajax_add_to_cart:after {
    -webkit-transform: rotate(90deg);
    -moz-transform: rotate(90deg);
    transform: rotate(90deg);
}
a.button.product_type_simple.add_to_cart_button.ajax_add_to_cart:hover{ 
    opacity: 1;
    background-color: #000;
}