I am using drupal_add_css() and drupal_add_js() to add CSS and JavaScript files to my Drupal site. I am doing this in a module called control so th
drupal_add_css()
drupal_add_js()
At the point your CSS/JS is needed, you can call it with drupal_add_css/js. You can also use it in the hook_init(), if your module is used on every page.