Learn Croatian: To što nema struje otežava posao kada pada mrak. - The fact that there is no electricity makes the work difficult when it gets dark.

To što acts as a compound subject here, standing in for the entire clause nema struje (there is no electricity). In English, we usually translate this structure as "The fact that...". While you might occasionally hear just što in casual speech, starting the sentence with To što clearly packages the whole idea into a single grammatical subject for the main verb, otežava (makes difficult).

Why is struja in the genitive case (struje)?

This is a quick refresher on a common Croatian construction for expressing the absence or lack of something. When the verb nemati (literally "to not have") is used impersonally to mean "there is no," the thing that is missing must be in the genitive case. So, "there is no electricity" becomes nema struje.

How is the verb otežava formed, and what does it literally mean?

Otežava comes from the imperfective verb otežavati. It is built from the adjective root težak (heavy or difficult). Adding the prefix o- and the suffix -avati turns it into a verb meaning "to make heavy" or "to make difficult." So literally, the lack of electricity "makes the work heavy."

In English we say "when it gets dark", but how is kada pada mrak structured literally?