I believe Croatia will play as they did it before, They will try to gamble on a Penalty kick. As we know how hard it when they get a win in 90' because the material player is not enough to create a score and face-to-face with Brazil players. I guess Croatia will play defensively in 90', so if they try to force and change the strategy, they will do the counter-attack strategy in extra time even if only 1 or 2 players are on the front because the rest is guard back to defense.
Penalty kicks are always risky for all teams, not only Croatia. I am sure that if possible, Croatia will try to win this match within 90 minutes (best) or 120 minutes but not want to go to another penalty kick.
Their team are no longer young especially their key players like Luka Modric or Ivan Perisic. We saw in the match with Japan that both Modric and Perisic were replaced in the first extra half because they were no longer able to run well enough to compete with Japanese players. Croatia need them not only for attacking but also for proactive defense.
Will their defence be able to cope with the pressure of attack that the Brazilian team will apply throughout the game? Croatia is an ageing team, their players are experienced but they are not capable of running around with maximum agility for 90 minutes against a team like Brazil therefore their strategy is limited.
Brazil have many players can make Croatia surprised but it is on the paper only. So far in this match, after a full first half, Brazil did not find a way to get closely to Croatia goalkeeper. Only a good combination between Richarlison and Vini Jr. That is a most considerable chance for them in the first half and it is not good enough to be called as a real chance.
Croatia will mainly defend within the match and patiently wait for counter attacking. We saw they did tried some times in the first half and in the second half, very likely that Brazil will attack more seriously. That will bring more opportunities for Croatia but of course they must keep their defense strongly first.