[CrOS Wallpaper] Increase contrast in wallpaper control colors

The color contrast between text+icon and the background for the
inactive state for the "Center" and "Center Cropped" buttons in the
Wallpaper modal[1] is low enough to cause accessibility issues for vision
impaired users at a ratio of 3.61 (compare to the minimal acceptable
ratio of 4.5 to meet W3C guidelines).

The contrast provided by the new color for both the text and icon, i.e.
Google Grey 700 aka #5F6368 aka rgb(95, 99, 104), provides an acceptable
ratio of 6.05.

[1] http://screen/hKAXfVsRLVn

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Result of this change: http://screen/dE3ipM3e1fA

Note: newly colored text/icon in red rectangle

Bug: 910362
Change-Id: Ica3b7b484f5ad64a83b259f9fa7c4d3e92c957df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1670358
Commit-Queue: Jordy Greenblatt <jordynass@chromium.org>
Reviewed-by: May Lippert <maybelle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671402}

chrome/browser/resources/chromeos/wallpaper_manager/css/wallpaper_manager.css

@@ -809,7 +809,7 @@ html[dir='rtl'] #current-wallpaper-more-options {
 
 #current-wallpaper-more-options #center,
 #current-wallpaper-more-options #center-cropped {
-  color: rgb(128, 134, 139);
+  color: rgb(95, 99, 104);
 }
 
 #current-wallpaper-more-options #center.disabled,