Why does Trunks have his hair parted to the side, but Vegeta has a widow's peak? Shouldn't Trunks have some of the same features as Vegeta, just like Gohan inherited Goku's features?
Whereas Gohan clearly inherited his looks from his father, Trunks appears to have inherited his looks from his mother, Bulma.
Here's a side-by-side comparison of Trunks and (a fanart of) Bulma as she appears in the Buu Saga. You can see they have very similar hairstyles - short bob cuts with centre-partings - and almost identical eyes:
Granted, their hair isn't exactly the same - and Bulma appears to change hairstyles a lot - but Gohan's hair is also slightly different to Goku's, if you look carefully at the spikes.