There's a window of 4 hours (often referred to as "grace period") after a question being closed in which answers can still be posted.

The "Post Your Answer" button and the box in which to type your answer are hidden, but answers are still being accepted. For example, if you've started writing an answer before the question got closed (and yes, there are (or at least [used to be](https://meta.stackexchange.com/questions/38228/incorrectly-able-to-answer-a-closed-question#comment604300_44634)) ways around that so you can even start writing your answer after it was closed).

Recommended reading material would be on Meta Stack Exchange: [here](https://meta.stackexchange.com/q/38228/269301), [here](https://meta.stackexchange.com/q/210295/269301), [here](https://meta.stackexchange.com/q/91922/269301), [here](https://meta.stackexchange.com/q/4683/269301) and [here](https://meta.stackexchange.com/q/261039/269301).

[meta-tag:status-bydesign]