Hi @GLaHeRa
OCS 2.x is semi-compatible with OJS 2.x themes, but not e.g. OJS 3.x themes. So I recommend you study OJS2 thems and how it is possible achieve what you want.
In forum we have some examples of customization in OJS2, that you may read and attempt to apply in OCS2.
See here:
Hope it helps
Regards,
Israel Cefrin
Public Knowledge Project Team