Escaping <?php problems

Hi! Your plugin is very good – it is simple and sufficient.

I have not studied PHP and I ask for help in solving my problem. The Code Editor requires escaping < for <?php. I have tried many escaping options, but I have not achieved the result. What should I wrap < for the code to become correct for the shortcode?

This is my code:

<div class="sitemap">
	<h2 class="sitemap-series">Series</h2>
		<?php $variable = wp_list_categories('taxonomy=series&echo=0&show_count=1&orderby=term_group&order=ASC&hide_empty=1&use_desc_for_title=1&child_of=0&feed=/RSS&title_li=&depth=0&current_category=0&pad_counts=1&walker=Walker&hide_title_if_empty=false&separator=');
		$resultStr = str_replace(array("(", ")"), array("<font color='#000000'>", "</font>"), "$variable");
		echo $resultStr;
		?>
</div>

Thanks!