Drupal Ctools Responsive Modal

responsive-modal.css

/* Override inline dom styles from modal.js */
#modalContent {
  position: fixed !important;
  top: 12% !important;
  bottom: 12% !important;
  right: 4% !important;
  left: 4% !important;
}
/* Limit max width to 1000px */
div.ctools-modal-content {
  width: 100% !important;
  margin: 0 auto;
  max-width: 1000px;
}
div.ctools-modal-content .modal-content {
  width: 100% !important;
}

template.php

/**
 * Implementes template_preprocess_html().
 */
function mytheme_preprocess_html(&$variables) {
  // Override ctools modal.css
  $css = drupal_add_css();
  foreach($css as $key => $value) {
    if (strpos($key, 'ctools/css/modal.css') !== FALSE) {
      drupal_add_css(drupal_get_path('theme', 'mytheme') . '/css/responsive-modal.css');
    }
  }
}