A huge number of international reference styles can be used in Zotero. The styles are created in the CSL programming language and are shared with e.g. Mendeley. You can get more styles under Edit -> Settings -> Cite -> Get additional styles.
Another way of adding styles is downloading and installing csl-files. Below are some University of Jyväskylä departmental styles available for download.
How to install: Right-click one of the links below and choose "Save link as". You should be able to download a file called "university-of-jyvaskyla-department-of-chemistry-eng.csl" or "tuulatutkija.csl". When you try to open the file, it should install automatically to Zotero. If this doesn't work, go to Zotero and choose Edit -> Settings -> Cite -> +, and add the correct file.
Department of Chemistry -style
Faculty of Sport Sciences -style (Tuula Tutkija)