Hi Deixi Carreño,
Let me clear you one thing, for Cloud based version, customization to an extent is possible. Beyond that you need Jive Support Existence.
For all customized Codings, whether it is HTML, FTL, Jquery, CSS which is customized, you need to give your clubbed files for the same to Jive Support. They will update for you.
On Your own, it is not possible to do the same. !
Please refer : Where to add Custom CSS file in Jive SBS 220.127.116.11 8c4?
Let me know if you have more queries. Hope it helps!