Hi,
It is a problem with the CSS of your template and the ".modal" rules.
You have to edit your CSS in order to fix it by replacing ".modal" by "div.modal".
We are working on the migration of the latest popup buttons in order to skip this compatibility problem.
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.