Learn Croatian: Gledaš kroz prozor, ali vani se vozi traktor. - You look through the window, but a tractor is being driven outside.

This is because ali (but) is a coordinating conjunction. Unlike subordinating words (like da or ako), coordinating conjunctions such as a, ali, nego, and ili do not count as the first position for clitics. The clitic se ignores ali and attaches to the first actual word of the second clause, which is vani.

How does se vozi traktor translate to "a tractor is being driven"?

The word se here creates a reflexive passive construction. Literally, it says "a tractor drives itself," but Croatian uses this structure frequently to express that an action is happening without mentioning who is actually performing it.

Why does prozor look like it is in the nominative case after kroz?

The preposition kroz (through) always requires the accusative case. Because prozor (window) is a masculine inanimate noun, its accusative form is identical to its nominative form, so it doesn't change its ending here.

Why use vani instead of izvan for "outside"?