What did the elf look like
Answers
As you specify Tolkien’s universe in your list of tags, I’m assuming Tolkien style elves. In the Tolkien Legendarium they are regarded as tall and pale with elegant features and slightly pointed ears. The translucent paleness is likely due to the fact that the Elves first arose in the days before sun and moon and initially lived far from the only sources of celestial light in Arda (The Two Trees, and later the Two Lamps, before the Sun and Moon were created) and even in latter days they tend to prefer the night to the day.
Further note, Elves and Men in Tolkien’s legendarium are biologically the same species and their differences are primarily spiritual in nature. (Elven souls are bound to Arda and won’t leave even after death, sometimes even reincarnating. Souls of Men are free to leave the world to explore other realms beyond Arda and thus do not suffer the weariness and fading of elves, but do die of old age…death is originally considered a gift and a result of them being unchained to the Fate of Arda and able to do their own thing.)
This is why Elrond’s title of “Half-Elven” isn’t a descriptor of kind but just an acknowledgement of his heritage. Elrond is an Elf despite one of his parents being of Men (I forget which) because he is an immortal bound to the fate of Arda and will eventually fade. His three children are Men because they chose the freedom of the Secondborn. Even though their lifespans are extremely long they do have lifespans and will eventually die.