If you want to add a style sheet for the Regular Labs (formerly no number) Modals pop-up to use, you need to do the following.

There are three steps to using an additional style sheet for the Modals pop-up window to use.

  1. Add modals.php file to the directory of the template you're using.
  2. Create a php file (session_modal.php) that contains your CSS.
  3. Modify the "<link rel " line in modals.php to point to your php css file.

modals.php file

<?php defined('_JEXEC') or die;
?>
<?php if (JFactory::getApplication()->input->get('iframe')) : ?>
    <?php
    $this->language  = JFactory::getDocument()->language;
    $this->direction = JFactory::getDocument()->direction;
    ?>
    <!DOCTYPE html>
    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="<?php echo $this->language; ?>" lang="<?php echo $this->language; ?>"
          dir="<?php echo $this->direction; ?>">
    <head>
        <jdoc:include type="head" />
    </head>
    <body class="contentpane modal">
    <jdoc:include type="message" />
    <jdoc:include type="component" />
    </body>
    </html>
<?php else: ?>
    <?php
    require_once JPATH_LIBRARIES . '/regularlabs/helpers/parameters.php';
    $parameters = RLParameters::getInstance();
    $config     = $parameters->getPluginParams('modals');
        echo '<link rel="stylesheet" type="text/css" href="/templates/rt_anacron/css/session_modal.php">';
    ?>
    <?php if ($config->load_head) : ?>
        <jdoc:include type="head" />
                
    <?php endif; ?>
    <jdoc:include type="message" />
    <jdoc:include type="component" />
<?php endif; ?>

session_modal.php

<?php header("Content-type: text/css; charset: UTF-8"); ?>
    #cboxLoadedContent {}
    #cboxContent {}
    H2 {}