Modifica el estilo del shortcode del botón de compra.

add-to-cart-shop-style.php

add_filter( 'woocommerce_loop_add_to_cart_link', 'apply_add_to_cart_shop_style' );
function apply_add_to_cart_shop_style(){
	global $product;

	if( !is_shop() && !is_product() ){

		echo sprintf( '<a href="%s" rel="nofollow" data-product_id="%s" data-product_sku="%s" data-quantity="%s" class="%s_%s button alt">%s</a>',
			esc_url( $product->add_to_cart_url() ),
			esc_attr( $product->id ),
			esc_attr( $product->get_sku() ),
			esc_attr( isset( $quantity ) ? $quantity : 1 ),
			esc_attr( $product->product_type ),
			$product->is_purchasable() && $product->is_in_stock() ? 'add_to_cart_button' : '',
			esc_html( $product->add_to_cart_text() )
		);
	}
}