Here is what it looks like (taking examples from Callouts - Obsidian Help):
{{< callout "info" >}}
Here's a callout block. It supports Markdown, Wikilinks, and embeds!
{{< /callout >}}
{{< callout type="tip" summary="Callouts can have custom titles" >}}
Like this one
{{< /callout >}}
{{< callout type="tip" summary="Title-only callout" />}}
{{< callout type="faq" fold="-" title="Are callouts foldable?" >}}
Yes! In a foldable callout, the contents are hidden when the callout is collapsed
{{< /callout >}}
{{< callout type="question" title="Can callouts be nested?" >}}
{{< callout type="todo" title="Yes!, they can." >}}
{{< callout type="example" title="You can even use multiple layers of nesting." />}}
{{< /callout >}}
{{< /callout >}}
{{< callout type="done" title="Callouts with markdown" >}}
Before {{< callout type="todo" title="Yes!, they can." >}}
**Before**
{{< callout type="example" title="You can even use multiple layers of nesting." >}}
**_Inside_**
{{< /callout >}}
**After**
{{< /callout >}}
After
{{< /callout >}}
{{< callout "note" "+" >}}
A note callout
{{< /callout >}}
{{< callout "abstract" "+" >}}
A abstract callout
{{< /callout >}}
{{< callout "summary" "+" >}}
A summary callout
{{< /callout >}}
{{< callout "tldr" "+" >}}
A tldr callout
{{< /callout >}}
{{< callout "info" "+" >}}
A info callout
{{< /callout >}}
{{< callout "todo" "+" >}}
A todo callout
{{< /callout >}}
{{< callout "tip" "+" >}}
A tip callout
{{< /callout >}}
{{< callout "hint" "+" >}}
A hint callout
{{< /callout >}}
{{< callout "important" "+" >}}
A important callout
{{< /callout >}}
{{< callout "success" "+" >}}
A success callout
{{< /callout >}}
{{< callout "check" "+" >}}
A check callout
{{< /callout >}}
{{< callout "done" "+" >}}
A done callout
{{< /callout >}}
{{< callout "question" "+" >}}
A question callout
{{< /callout >}}
{{< callout "help" "+" >}}
A help callout
{{< /callout >}}
{{< callout "faq" "+" >}}
A faq callout
{{< /callout >}}
{{< callout "warning" "+" >}}
A warning callout
{{< /callout >}}
{{< callout "caution" "+" >}}
A caution callout
{{< /callout >}}
{{< callout "attention" "+" >}}
A attention callout
{{< /callout >}}
{{< callout "failure" "+" >}}
A failure callout
{{< /callout >}}
{{< callout "fail" "+" >}}
A fail callout
{{< /callout >}}
{{< callout "missing" "+" >}}
A missing callout
{{< /callout >}}
{{< callout "danger" "+" >}}
A danger callout
{{< /callout >}}
{{< callout "error" "+" >}}
A error callout
{{< /callout >}}
{{< callout "bug" "+" >}}
A bug callout
{{< /callout >}}
{{< callout "example" "+" >}}
A example callout
{{< /callout >}}
{{< callout "quote" "+" >}}
A quote callout
{{< /callout >}}
{{< callout "cite" "+" >}}
A cite callout
{{< /callout >}}

See https://blog.remibardon.name/en/dev/callouts/ for a render.