Hi,
It's a good idea to add your CSS in the custom.css of your template.
If you can, it's best to keep using the default of the frontend CSS of HikaShop so that the get the new CSS code we add for each new version of HikaShop (for the new features, etc).
The CSS you added in the frontend CSS of HikaShop was probably overridden by your template CSS as it is loaded after it on your pages while the custom.css of the template is loaded after the template's CSS. That can usually be overcome with !important but it you can not use !important it's even better.