Add category body class to The Events Calendar category archives

functions.php

<?php

add_filter( 'body_class', 'tec_archive_body_class' );

function tec_archive_body_class( array $classes ) {

	if (is_tax( 'tribe_events_cat' ) ) {
		$classes[] = 'rg-events-category';
	}

	return $classes;
}