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Gets or sets the line style applied to the border collection.
Setting this property applies the specified line style to the outer and inside borders in the collection. To set a diagonal border, use this[BordersIndex] with DiagonalDown or DiagonalUp.
BorderLineStyle LineStyle { get; set; }
Property LineStyle As BorderLineStyle
IBorders borders = worksheet.Range["B2:E6"].Borders;
borders.LineStyle = BorderLineStyle.DashDot;
BorderLineStyle lineStyle = borders.LineStyle;