I’d like to develop a generalizable solution for creating etched lines. The goal is to be able to not have to manually pick closely related colors for every color scheme where I want etching. The issue seems that the color of the indented part in relation to the color of the background is somewhat critical for creating the 3 dimensional effect.
Below is an example in blue (the lines above the comment bubble/underneath the number “11”). I think I need to use box-shadow but not sure if this is the best way.
If box-shadow is what I should use, does anyone know how to set its CSS values such that would would work for say a gray line would also work for say a blue line?

You could use borders with semi-transparent black/white colors (using
rgba) that will darken/lighten the underlying color.Example at http://dabblet.com/gist/4182495
Adding pseudo elements with
:after/:beforegives you extra power in adding second level borders etc..