Collapsing headers adds a new line

[AlessioQuercia]

Issue: making an header collapsible adds a white new line, and then the header summary. To reproduce the issue, you can use the following snippet:

<details><summary> <h1> Header 1 </summary>

Just a test.
</details>

As far as I noticed, this issue is different Markdown editors, except for GitHub, GitLab. I guess it depdends on the different markdown formatting style used by these two. Is it possible to fix this issue?

Below you can see that GitHub formats this snippet correctly:

Header 1

Just a test.

[HemanthPaila]

Hi there,

I want to contribute to this project and take on this issue as my first task. Could you please assign it to me? I am excited to work towards resolving it and will keep the team updated on my progress.

Thanks!

[jackycute]

Hi there,

I want to contribute to this project and take on this issue as my first task. Could you please assign it to me? I am excited to work towards resolving it and will keep the team updated on my progress.

Thanks!

You can open a PR anytime.