1. I don't see the page where you're attempting this (link hidden and for HikaShop only?), don't know where exactly you've placed your code, and you don't tell what exactly doesn't work, or symptoms, errors or so. There could be many reasons for it, but how to tell without seeing it.
2. Again, you seem to already have separate wrapping divs, and different classes (or IDs) of these divs do let you target the elements inside individually, even if the elements have identical classes. It would lead too far, and doesn't belong here, to explain these CSS basics here, sorry, but there is plenty all over the web where you can learn CSS.
3. Depends on your specific case, eventually. Hint: see how it's done elsewhere in your site. Anyway, it's not HikaShop-related, so this sort of modifications can hardly be dealt with here.
Bottom line:
For certain modification/customizations you can receive help here, but you need to tell the whole story on what/where/how, especially if you've already started something, and make it visible, e.g. with a link.
Other modifications are beyond of what can be supported, either because it's too extensive, or it's not related to HikaShop.
So, again, a link to a page where one could see the result of what you've done so far would be a good start.