Thin separator lines

In shortdoc buffers we have separator-line and then there is also the fill-column-indicator face. I use these two settings, which could very well also be part of the theme, at least for the graphical UI.

(set-face-attribute 'separator-line nil :inherit 'shadow :background nil :underline t :height 1)
(set-face-attribute 'fill-column-indicator nil :height 1 :inherit 'shadow :inverse-video t)

Instead of shadow one could use a different color. The fill-column-indicator change has one small oddity. If you move the cursor over the indicator character it will have a width of only a single pixel. But besides that I haven't seen negative effects since as soon as you type beyond the fill column, the character will be replaced. Adjusting the face attribute of fill-column-indicator seems to be the only way to get a thin line. Box drawing characters are not an option since they will break with line-spacing>0.