A GridLinesStyleEnum expression that specifies the style to show the chart's
vertical gridlines.
By default, the GridLineStyle property is exGridLinesDot.
The GridLineStyle property has effect only if the chart's DrawGridLines
property is not zero and one of the level's DrawGridLines
property is True. Use the GridLineColor
property to specify the color for vertical grid lines. Use the DrawTickLines
property to specify whether the grid lines between time units in the level are
visible or hidden