Hi,
Please use this custom css code:-
ul.products li.product a.quick-view-button, .woocommerce p.cart a.add_to_cart_button, .lost_reset_password p.form-row input[type="submit"], .track_order p.form-row input[type="submit"], .change_password_form p input[type="submit"], .woocommerce form.register input[type="submit"], .woocommerce .wishlist_table tr td.product-add-to-cart a, .woocommerce input.button[name="save_address"], .woocommerce .woocommerce-message a.button, .woocommerce .quantity, .woocommerce-page .quantity, .woocommerce form.cart .yith-wcwl-add-to-wishlist a, .woocommerce-checkout .login input[type="submit"], .woocommerce button[type="submit"], .my-account-login-wrap .login-wrap form.login p.form-row input[type="submit"], .products .product.buy-btn-visible > .product-actions .add-to-cart-wrap > a {
border-color: #000 !important;
}
.woocommerce form.cart button.add_to_cart_button:hover, #jckqv .cart .add_to_cart_button:hover, #jckqv .cart .yith-wcwl-add-to-wishlist a:hover, .woocommerce .single_add_to_cart_button:hover, .woocommerce .single_add_to_cart_button.button.alt:hover{
border-color: #000 !important;
}
Thanks
Mohammad