With SunSed you can create your own custom HTML tags and abstract all the CSS and JS then use Sundown to call that tag (or the HTML syntax).

    <s:tag name="note">
        <div style="color:red;">
            Note: {{@content}}!!
        </div>
    </s:tag>

And then call your new tag using the HTML syntax or Sundown:

    <note>Sundown is awesome ;)</note>
    :note Sundown is awesome :)