You can create a custom PayPal payment page style. For more information check here:
https://www.paypal.com/hk/cgi-bin/webscr?cmd=p/mer/cowp_summary-outside
If you have more than one shop, you might want X-Cart to use a specific style other than the default one. Simply add the following line to /payment/ps_paypal.php for PayPal, and /payment/ps_paypal_pro_us.php for PayPal Pro Express Checkout
Code:
++$fields["page_style"] = "PAYPAL STYLE NAME";
func_create_payment_form("https://$pp_host/cgi-bin/webscr", $fields, 'PayPal');
Tested working for v4.4 and v4.5