[WordPress] Allow more HTML tags and attributes in post context.

wp-allowed-html.php

<?php
/**
 * Filter allowed HTML elements.
 *
 * @param $allowedposttags
 * @param $context
 *
 * @return array
 */
function prefix_filter_allowed_html( $allowedposttags, $context ) {

	if ( $context == 'post' ) {
		$allowedposttags['table']['background'] = true;
	}

	return $allowedposttags;
}

add_filter( 'wp_kses_allowed_html', 'prefix_filter_allowed_html', 10, 2 );