Here is a _simple_ hack that uses a tab to add a bottom line.
The screen capture is here:
https://peertube.social/videos/watch/2fe159c3-51fb-46a7-b7c0-7b218720bc03- Show the Properties palette
- Set the frame width to 70 mm
- Add a paragraph after the title
- Hide the Properties palette
- Show the text palette
- Text Properties > Column & text distances > Tabulators
- Define a tabulator at 69 mm (one mm less than the frame width), right aligned
- Activate the "show control chars"
- Insert a tab character
- Colour & Effects:
- Underline
- Set the thickness for the underline
- Set the color for the paragraph with the tab
- Shrink the line spacing
If you know the width of the column, you can create a style with the right tab, the color and the line height already defined.
You can find attached the final .sla file.