CODE EXAMPLE FOR PHP

woocommerce custom sale banner, sash

add_filter('woocommerce_sale_flash', 'ydcoza_custom_sales_badge');
function ydcoza_custom_sales_badge() {
  $url = site_url().'/wp-content/uploads/2021/03/best_seller_sash.png';
  $img = '<div class="ydcoza-sale-banner"><img src="'. $url .'"></img></div>';
  return $img;
}