a function that loads up a themeroller stylesheet for the calendar. Can be placed in a theme's functions.php file

calendar-theme.php

<?php
add_action('wp_enqueue_scripts', 'add_calendar_themeroller_stylesheet');
function add_calendar_themeroller_stylesheet() {
  global $org_options;
	global $espresso_calendar;
		$page_array = explode(',', $espresso_calendar['calendar_pages']);
		//print_r($page_array);
		if ($espresso_calendar['calendar_pages'] != 0) {
			if (!is_page($page_array)) {
				return;
			}
		}

		//Define the path to the ThemeRoller files
		if (file_exists(EVENT_ESPRESSO_UPLOAD_DIR . "themeroller/index.php")) {
			$themeroller_style_path = EVENT_ESPRESSO_UPLOAD_URL . 'themeroller/';
		} else {
			$themeroller_style_path = EVENT_ESPRESSO_PLUGINFULLURL . 'templates/css/themeroller/';
		}


		//Register the ThemeRoller styles
		if !is_admin()) {

			//Load the themeroller base style sheet
			//If the themeroller-base.css is in the uploads folder, then we will use it instead of the one in the core
			if (file_exists(EVENT_ESPRESSO_UPLOAD_DIR . 'themeroller/themeroller-base.css')) {
				wp_register_style('espresso_themeroller_base', $themeroller_style_path . 'themeroller-base.css');
			} else {
				wp_register_style('espresso_themeroller_base', EVENT_ESPRESSO_PLUGINFULLURL . 'templates/css/themeroller/themeroller-base.css');
			}
			wp_enqueue_style('espresso_themeroller_base');

			//Load the smoothness style by default<br />
			if (!isset($org_options['themeroller']['themeroller_style']) || empty($org_options['themeroller']['themeroller_style']) || $org_options['themeroller']['themeroller_style'] == 'N' ) {
				$org_options['themeroller']['themeroller_style'] = 'smoothness';
			}

			//Load the selected themeroller style
			wp_register_style('espresso_themeroller', $themeroller_style_path . $org_options['themeroller']['themeroller_style'] . '/style.css');
			wp_enqueue_style('espresso_themeroller');
		}
}
?>