Snippet to change Estimated Delivery date style on cart page using Estimated Delivery Date Plugin for WooCommerce by PluginHive - https://www.pluginhive.com/product/estimated-delivery-date-plugin-woocommerce/

function.php

/**
 * Snippet to change Estimated Delivery date style on cart page.
 * Created at : 24 Aug 2018
 * Updated at : 24 Aug 2018
 * PluginHive Plugins : https://www.pluginhive.com/plugins/
 * Gist Link : https://gist.github.com/xadapter/23dc533d6e166b76fa25d0c8d4fd0f5b
 */

add_filter( 'xa_estimated_delivery_cart_checkout_page_html_formatted_date', function($date) {
	$date = str_replace( '<td', '<td style="font-weight: bold;"', $date);
	return $date;
} );