I used ☐
(☐) for [ ]
and ☑
(☑) for [x]
and it works for marked.js which says it is compatible with Github markdown. I based my solution on answers for this question. See also this informative answer.
Update: I should have mentioned that when you do it this way, you do not need the <ul>
, e.g:
| Unchecked | Checked |
| --------- | ------- |
| ☐ | ☑ |