showdown-container 
Fenced container plugin for the showdown markdown parser, idea copied from markdown-it-container
This extension allows you to create block level containers:
::: some-class
*Some text*
:::
Which will be rendered as:
<div class="some-class">
<em>Some text</em>
</div>
Usage
var Showdown = require('showdown');
var showdownContainer = require('showdown-container');
var converter = new showdown.Converter({ extensions: [showdownContainer] });
var converter = new showdown.Converter({ extensions: ['container'] });
Future
Installation
$ npm install --save showdown-container