Hi,
Right, the feature is not yet available in the current package.
You can find the HikaMarket CSS file in the folder "media/com_hikamarket/css/frontend_default.css"
Like HikaShop and his override system, HikaMarket will have in the next release the same kind of editing feature in his configuration panel.
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.