Hi,
The issue is related to the "style_default.css" and your CSS parser.
Because you're using the "style_default.css", you have some old rules applied.
And between "hikashop.css" and "style_default.css", some rules are duplicated (like the grid layout).
But with your CSS parser, the CSS content is minified and the duplicate is removed.. The problem is that, the second rules are removed and it generate an issue regarding the ordering of the rules.
So, the best would be to not use the "style_default.css" content but to create your own style CSS file so you can only put the rules that you need for your website.
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.