https://devnet.kentico.com/docs/7_0/devguide/index.html?common_web_part_properties.htm
HTML Envelope
Content before
HTML content placed before the web part. Can be used to display a header or add some encapsulating code, such as <div> or <table> elements to achieve the required layout.
<table style="background-color: red" align="right">
<tr>
<td>
Content after
HTML content placed after the web part. Can be used to display a footer or close the tags contained in the ContentBefore value, such as </div> or </table> elements.
</td>
</tr>
</table>
before和after可以前后拼接，实现html和css
https://devnet.kentico.com/docs/7_0/devguide/index.html?web_part_containers_overview.htm