I was a Confluence user many years ago. I can remember that I used the so called callouts many times. In my search for an implementation in Markdown I found out that Markdown has an extension for this called admonitions.

attention
caution
danger
error
hint
important
note
tip
warning

Note

Here is my markdown content.

Attention

Here is my markdown content.

Error

Here is my markdown content.

Warning

Here is my markdown content.

Tip

Here is my markdown content.

Caution

Here is my markdown content.

Danger

Here is my markdown content.

Important

Here is my markdown content.

Hint

Here is my markdown content.

TODO: describing the Howto.