[css-color] Improve descriptions of system colors

[tabatkins]

On Sun, 18 Feb 2001 dbaron wrote:

Until today, I never understood why there were so many, seemingly
rendundant, system colors for 3-D objects in section 18.2 of CSS2.
Today I was forced to understand how the Windows colors work so that I
could correct Mozilla's system colors implementation in the GTK port.

I think we should (whether for CSS2 errata or for CSS3) use clearer
definitions of these colors so that one doesn't have to
reverse-engineer the Windows system color APIs to figure out what the
CSS system color definitions mean. (See [1] and [2] for a description
of this API.)

So that other people implementing system colors on non-Windows
platforms don't have to do the same reverse-engineering that I
benefited from and puzzling over the definitions that I did, I propose
the following new definitions as a start to clearer definitions (but
see below):

ButtonFace
The face background color for 3-D elements that appear 3-D due to
one layer of surrounding border.

ButtonHighlight
The color of the border facing the light source for 3-D elements
that appear 3-D due to one layer of surrounding border.

ButtonShadow
The color of the border away from the light source for 3-D elements
that appear 3-D due to one layer of surrounding border.

ThreeDDarkShadow
The color of the darker (generally outer) of the two borders away
from the light source for 3-D elements that appear 3-D due to two
concentric layers of surrounding border.

ThreeDFace
The face background color for 3-D elements that appear 3-D due to
two concentric layers of surrounding border.

ThreeDHighlight
The color of the lighter (generally outer) of the two borders facing
the light source for 3-D elements that appear 3-D due to two
concentric layers of surrounding border.

ThreeDLightShadow
The color of the darker (generally inner) of the two borders facing
the light source for 3-D elements that appear 3-D due to two
concentric layers of surrounding border.

ThreeDShadow
The color of the lighter (generally inner) of the two borders away
from the light source for 3-D elements that appear 3-D due to two
concentric layers of surrounding border.

I'm pretty sure these descriptions fit the way system colors are
implemented across-platforms (Windows, Mac, and soon to be GTK) in
Mozilla. Are they implemented this way in MacIE? (I assume this
is how they're implemented in WinIE, since the colors come straight
from the Windows API.)

I don't think these descriptions correctly describe how these colors
are used to represent depressed buttons, though. (That's why I said
"generally inner" and "generally outer" rather than "inner" and
"outer".) Any thoughts about how to improve them?

[tabatkins]

All of these definitions were folded in at least seven years ago; archaeology is too annoying to deal with past that point to find the exact commit.