line-width. another important issue is the erasing-color (that is, the border-bottom-color). its color should match that of the background.
this only demonstrates a rising line, but can be as easily used for a falling line by using right borders and a negative left for the erasing triangle.
nothing is perfect, and this technique is not even close to being so.
background must be solid - i can't think of a way to allow the lines on top of an image background.
cannot draw horizontal and vertical lines. they're easy to draw, but it's less pretty (for the programmer).
must distinguish between rising and falling lines - again, less pretty.
i presented here a novel method for 