While WCM doesn't allow for adding borders to individual apps, you can fake it by adding table code, and putting your stuff in the table.

This is as simple as copying and pasting the following into HTML view of your app:

<table style="width: 100%;" cellpadding="5;" border-color: #fe6c00;" border="3;" align="center">
<tbody>
<tr>
<td>

(YOUR STUFF GOES HERE)

</td>
</tr>
</tbody>
</table>

Understanding:
The parameters in the code above are quite extensible. Here's what they do:

<table> - This tag tells the page to begin creating a table. The matching tag to CLOSE the table is </table>.

style="width: 100%;" - This parameter is relative, and tells the table to take up 100% of whatever horizontal space it inhabits. The width command can also be applied to cells, to divide up the space inside the table to whatever amounts suit you.

cellpadding="5;" -  This number determines how much "air" there is between the lines defining each cell and any inserted material. (Note: to add space between cells and columns, you'd want cellspacing, which works the same way.)

border="2;" -  This tells the table to show its outer border, and how thick to make it. The larger the number, the thicker the border.

border-color: #0000ff;" - This governs the color of the border, defined in hex. How do you know what to tell it to get the color you want? Find your colors here.

align="center" - You really only need this if the width of the table is less that 100%. Other arguments are "left" and "right".

<tbody> - This one needs to come right after the <table> tag and its parameters. Its corresponding closing tag, </tbody>, goes right before the closing </table> tag.

<tr> - This opens a table row, which encapsulates cells, and closes with </tr>.

<td> - The tag that opens a tabele cell (because everyone knows "cell" starts with "d"). It's corresponding closing tag is </td>. You can have any number of these inside a table row, to define colums.

Accordingly, the code above makes a table that looks like this: