Styling EE Custom Module

class Datetime_picker_ft extends EE_Fieldtype {
    
    /**
     * Constant that holds the folder name of the field type's css and js in the third_party themes folder
     *
     * @const string
     **/
    const THEME_DIR = 'datetime_picker';
    
    /**
     * Stores the state of whether the field type has been initialized before
     * @access protected
     * @static
     * @var bool 
     **/
    protected static $initialized = FALSE;
    
    /**
     * Stores the base url to the themes folder
     * @access public
     * @var string  
     **/
    public $theme_folder_url = '';

    /**
     * Holds general field type meta info
     * @access public
     * @var array  
     **/
    public $info = array(
        'name'        => 'Date/Time Picker',
        'version'    => '1.0',
        'author'     => 'Thomas Brewer @th3mus1cman',
    );
    
    
    /**
     * Constructor
     *
     * @access public
     * @param  void    
     * @return void
     * 
     **/
    public function __construct()
    {
        parent::__construct();
        
        $this->theme_folder_url = $this->EE->config->item('theme_folder_url');
    }
    
    
    /**
     * Handles the display of the field in the channel entry page
     *
     * @access public
     * @param  array $data    
     * @return string HTML 
     * 
     **/
    function display_field($data)
    {
        if (self::$initialized === FALSE)
        {
            //only need to add this stuff once...
            
            $timepicker_url             = $this->theme_folder_url.'third_party/'.self::THEME_DIR.'/jquery.timepicker.js';
            $slider_url                 = $this->theme_folder_url.'third_party/'.self::THEME_DIR.'/jquery.slider.js';
            $style_url                     = $this->theme_folder_url.'third_party/'.self::THEME_DIR.'/jquery.timepicker.css';
            
            $this->EE->cp->add_to_foot('<link href="'.$style_url.'" type="text/css" rel="stylesheet" />');
            $this->EE->cp->add_to_foot('[removed][removed]');
            $this->EE->cp->add_to_foot('[removed][removed]');
    
            self::$initialized = TRUE;
        }
        
        $js_config = json_encode(
            array(
                'timeOnly' => $this->settings['time_only'],
                'ampm' => TRUE,
            )
        );

        $js = <<< JS
            $('input[name=field_id_{$this->field_id}]').datetimepicker($js_config);
JS;
        $this->EE->javascript->output($js);
        
        if ((int) $data == 0)
        {
            $datetime = '';
        }
        else
        {
            if ($this->settings['time_only'])
            {
                $datetime = (is_numeric($data)) ? strtolower(strftime('%I:%M %p', $data)) : $data;
            }
            else
            {
                $datetime = (is_numeric($data)) ? strtolower(strftime('%m/%d/%Y %I:%M %p', $data)) : $data;
            }
            
            
        }
        
        return form_input(array(
            'name'    => $this->field_name,
            'id'        => $this->field_id,
            'class'    => 'datetime_picker',
            'value'    => $datetime
        ));
    }