In Costa Rica there is no particular traditional outfits in tourist places contrary to Guatemala or to Zanzibar for example. The country is relatively developed and we see everything.
However, it is evident that it is better to wear correct outfits. So forget about mini skirts or mini shorts especially if you are a single woman who travels.
Also, the naturism in Costa Rica is not necessarily viewed favorably so forget that while on vacation in Costa Rica.
To mingle more easily with the inhabitants of this beautiful country and avoid shocking them, whether in Costa Rica or elsewhere, be respectful of your clothing.