Create custom 'Add to cart' with wordpress woocommerce
Well, you can do it with ajax, you can redirect it to - '?add-to-cart=' and the item will get into the cart. so you will be able to design you'r button however you want ..
It only works in shop page this way. Try this for other pages:
$product = get_product(77);
echo "<a href='" . $product->add_to_cart_url() ."'>add to cart</a>";