Updated spec

Navigation
https://folio.googleplex.com/chrome-ux-specs-and-sources/Chrome%20Inner%20Pages/03-Settings/specs#%2FSPEC-settings_structure-navigation.png%3Fz=width&c=show

Colors
https://folio.googleplex.com/chrome-ux-specs-and-sources/Chrome%20Inner%20Pages/03-Settings/specs#%2FSPEC-settings_color.png%3Fz=width&c=show

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e233d14c7d5f89defc25a238157cdb58ca22e4d3

commit e233d14c7d5f89defc25a238157cdb58ca22e4d3
Author: dschuyler <dschuyler@chromium.org>
Date: Mon Mar 21 19:08:02 2016

[MD settings] change side nav text and icon color

This CL changes the color of the side nav icon and
color text to a slightly lighter grey.

BUG= 596143 

Review URL: https://codereview.chromium.org/1820533002

Cr-Commit-Position: refs/heads/master@{#382348}

[modify] https://crrev.com/e233d14c7d5f89defc25a238157cdb58ca22e4d3/chrome/browser/resources/settings/settings_shared_css.html