Markdown inside div blocks is not rendered on html export

Hi

As presented in this issue (Markdown no longer formatted in html div · Issue #4504 · jupyter/notebook · GitHub), I used to use html div tags to embed few lines of text of markdown to highlight part of a notebook.

The solution presented in the issue worked inside jupyter notebook/lab. The markdown lines display correctly but when I try to export the notebook to html, the code inside the div tags is not translated to html.

For example, here is the markdown cell in jupyter:

<div class="alert alert-success">

**Exercice :**
1. bla bla
2. bla bla

</div>

And this is the html file produced when I export the notebook to html:

<div class="jp-Cell-inputWrapper"><div class="jp-InputPrompt jp-InputArea-prompt">
</div><div class="jp-RenderedHTMLCommon jp-RenderedMarkdown jp-MarkdownOutput " data-mime-type="text/markdown">
<div class="alert alert-success">

**Exercice :**
1. bla bla
2. bla bla

</div>
</div>
</div>

I tried to add markdown="1" in the div block but it does not fix the issue.

Thank you for any help