Add the Buy on Kindle button near Add to Cart in WooCommerce PDP.

/**

* Snippet Name:	Add the Buy on Kindle button near Add to Cart in WooCommerce PDP.

*/

add_action('woocommerce_after_add_to_cart_button','add_kindle_button');

function add_kindle_button() {

    $kindle_button_url =  get_post_meta( get_the_ID(),'kindle_button_url',true);

    if ( isset($kindle_button_url) && filter_var($kindle_button_url, FILTER_VALIDATE_URL)) {

    	$style = 'style="background-color: #ff9900; color: #fff;';

    	$button = '<button ' . $style . ' type="button" class="button" >Buy on Kindle</button>';

    	echo '<a href="'.$kindle_button_url.'" target="_blank" rel="noopener">' . $button . '</a>';

    }   

}