Updated: Aug 16, 2020
granted that; even if; even though
Whatever the reason, they did not marry.
You should do your best in everything.
either way your still mistaken.
Note: にせよ and にしろ are used interchangeably. Also can mean whatever/whoever/whichever but generally meaning "even thou" or "even if"
For the 2nd sentence direct translation would be more close to saying "whatever thing you do, do your best" but a more summed up loose translation would be. "You should do your best in everything"But in translation there really is no exact result in this case simple is better. It could even be "whichever you do" as well.
These sentence examples have come from jisho.org
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