The Frame section in the General tab specifies the properties to use for the border around different objects to which a frame can be applied, such as legends, color scale bars, and map scale bars.
Change Frame properties in the General tab
The Type list specifies the type of border to use for the frame: None, Square, or Rounded. Setting this value to None shows no border. Fill properties cannot be applied to a frame when the Type is set to None. Setting the Type to Square creates a rectangle at the edge of the object at the Margin distance. Setting Type to Rounded creates a rounded rectangle at the edge of the object at the Margin distance.
Margin specifies the distance between the edge of the frame and the text or symbols within the framed object. Values are in inches or centimeters, determined by the page units.
Click the next to Line Properties to open the Line Properties section. Set the Style, Color, Opacity, and Width of the line to use for the frame.
Click the next to Fill Properties to open the Fill Properties section. Set the Pattern, Color, and other fill properties to use for the foreground and background of the framed area.