Learn Croatian: Kako je vokabular važan, tako je i gramatika. - Just as vocabulary is important, so too is grammar.

In the structure kako ..., tako i ... (just as ..., so too ...), the word i adds the meaning of 'also' or 'too'. It emphasizes the parallel between the two clauses. While you could technically just use tako, adding i is much more natural when showing that a second thing is equally true.

The adjective važan is masculine to match vokabular. Why isn't there a feminine adjective važna to match gramatika?

Croatian often drops words in the second half of a parallel sentence to avoid repetition, just like English does. The full second clause would be tako je i gramatika važna, but because the concept of being important is already established, leaving the adjective out makes the sentence flow much better.

Why does the verb je come immediately after kako and tako?

The verb je is an enclitic, meaning it is a 'weak' word that must take the second grammatical position in its clause. Since kako and tako take the first position in their respective clauses, je must be placed directly after them.

Could I use kao što instead of kako at the beginning of the sentence?