Sales Flash Gradient

sales-flash.php

<?php
    if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly
    global $post, $product;
    if ( ! $product->is_in_stock() ) return;
    $sale_price = get_post_meta( $product->id, '_price', true);
    $regular_price = get_post_meta( $product->id, '_regular_price', true);
    if (empty($regular_price)){ 
        $available_variations = $product->get_available_variations();
        $variation_id=$available_variations[0]['variation_id'];
        $variation= new WC_Product_Variation( $variation_id );
        $regular_price = $variation ->regular_price;
        $sale_price = $variation ->sale_price;
    }
    $sale = ceil(( ($regular_price - $sale_price) / $regular_price ) * 100);
?>
<?php if ( !empty( $regular_price ) && !empty( $sale_price ) && $regular_price > $sale_price ) : ?>
    <?php
        $R=floor((255*$sale)/100);
        $G=floor((255*(100-$sale))/100);
        $bg_style = 'background:none;background-color: rgb(' . $R . ',' . $G . ',0);';
    ?>
    <?php echo
        apply_filters( 'woocommerce_sale_flash', '<span class="onsale" style="'. $bg_style .'">-' . $sale . '%</span>', $post, $product );
    ?>
<?php endif; ?>