[StyleBox] that displays a single line. [StyleBox] that displays a single line of a given color and thickness. It can be used to draw things like separators. The line's color. The number of pixels the line will extend before the [StyleBoxLine]'s bounds. If set to a negative value, the line will begin inside the [StyleBoxLine]'s bounds. The number of pixels the line will extend past the [StyleBoxLine]'s bounds. If set to a negative value, the line will end inside the [StyleBoxLine]'s bounds. The line's thickness in pixels. If [code]true[/code], the line will be vertical. If [code]false[/code], the line will be horizontal.