Not rendered in GitHub style

It is rendered in most other styles though.

Not rendered in GitHub style

It is rendered in most other styles though.

I see the issue and will fix it in v3. For now, just add this to Settings->Style->Additional CSS:
#wrapper details>summary:first-of-type { display: list-item !important }
That should fix it for all syles.
(This is fixed for the next v3 beta update)