Hi,
You do not loose CSS, you have a PHP error which broke the page.
Please check the bottom of your page, an error could be display. If not, you would have to activate the debug mode in Joomla in order to see the PHP error.
At this moment we would be able to help you to fix it.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.