LibreOffice 7.5 Help
The Drawing Object Properties toolbar contains icons and combo boxes to define various line attributes.
Click the Line icon to open the Line dialog.
Click the Arrow Styles icon to select an arrow style for the right and left ends of a line.
Select a style from the Line Style box and specify the width in the Line Width box. A width of 0 corresponds to 1 pixel.
Select the line and arrow color in the Line Color box.