"It is late."
It's not really up for vote. Juanv asked a question, which is a good way to learn. There's not much to agree with though, as he used the wrong word.
Because “Esta tarde" means something completely different; it means “This afternoon."
It is commonly expressed that way, but the Duo computer probably does not want to see the optional 'ya'
"es el tarde" is incorrect, because "tarde" here is an adjective which doesnt need the article. Besides, when as a noun, "tarde" is feminine, so it should be "es la tarde", but then it'd be meaning "it is (the) afternoon' instead of "it is late".