adding custom css to the woocommerce email template

custom-css-to-woo-email-template.php

<?php

add_filter( 'woocommerce_email_styles', 'piweb_add_css_to_emails', 9999, 2 );
 
function piweb_add_css_to_emails( $css, $email ) { 
   $css .= '
      .pi-order-meta-date { font-weight:bold; color:#f00; }
      .pi-order-meta-time { font-weight:bold; color:#f00; }
   ';
   return $css;
}