Learn Croatian: Što god odlučiš, ja ću se složiti. - Whatever you decide, I will agree.

The particle god can be added to question words to give them an "-ever" or "any" meaning. Here, što (what) is paired with god to create što god (whatever). You will also see this pattern with tko god (whoever) and gdje god (wherever).

Why is odlučiš in the present tense if the agreement is happening in the future?

In Croatian, it is very common to use the present tense of perfective verbs like odlučiti (to decide) in dependent clauses that act as conditions for the future. Phrases starting with što god, ako (if), or kad (when) use this to mean "Whatever you (will) decide."

Why do ću and se come between ja and složiti?

Both ću (from the future tense) and se (from the reflexive verb složiti se) are enclitics. Enclitics are unstressed words that must jump to the second position in a clause. Since the pronoun ja takes the first spot, the enclitics must immediately follow it, strictly in the order of auxiliary verb first (ću), then reflexive pronoun (se).

Could I say sve što instead of što god here?