The pressure Hard adds
Hard looks far enough to reject many moves that win something immediately but fail on the next exchange. It also stops choosing deliberately weaker alternatives from a pool. You should expect loose pieces, exposed kings and optimistic sacrifices to be challenged more consistently, although this lightweight browser engine is not presented as tournament-strength software.
Spend time on candidate moves
In a critical position, name two or three serious candidates before calculating one line deeply. Start with forcing moves, then compare quiet improvements. The 3+2 recommendation creates genuine pressure while preserving a small amount for technical play. If you spend a minute, record what made that position worth the investment.
Review decisions, not just blunders
A Hard game is most useful when the post-game question is precise. Find the first position where your chosen move was based on only one candidate, or where you used substantial time without calculating the opponent's forcing reply. That decision-quality review teaches more than counting the final material balance.