When you add a line style to the Line Styles list, an item with no defined attributes is added under the group you select. Once added you can define the new line style's properties.
Access the line styles library. How to
In the Group window, select or create the group you want to add the line style to.
Select Line Style > Add Line Style, or right-click in the Line Style window and select Add Line Style.
In the Line Style Name edit box, type a name for the new line style.
From the Linetype
drop box, select a linetype for the line style, or click the Browse button
next to the Linetype drop box
to access the Linetypes dialog.
You can add or edit linetypes to suit
your needs.
Click the Color box in the Edit Line Styles dialog, then select the line color you want from the Color dialog.
Click OK. The line style is added to the library.