在ggplot2中，是否只能在一边修改条的边界?(颜色、厚度)

I know, 3D Barcharts are a sin. But i´m asked to do them and as a trade-off i suggested to only make a border with a slightly darker color than the bar´s on the top and the right side of the bar. Like that, the bars would have some kind of "shadow" (urgh) but at least you still would be able to compare them. I know, 3D Barcharts are a sin. But i´m asked t