Headings…

That box has a class of scbb-content-box, so it is fairly easy to style with some CSS. Unfortunately, it has some inline style (like a background-color) that should really be moved to the Custom CSS option instead, along with the the inline style for the span inside of it.

You can add this rule to your Custom CSS option to create a box:

.scbb-content-box {
   border: 2px solid #0000ff;
}

The first parameter creates a 2px wide border.
The second parameter creates a solid (instead of dashed) line as the border.
The third parameter is the color (blue).

Change any of these values to whatever you think would look the best.