[css-scrollbars-1] Remove light/dark values of scrollbar-color w3c#6438

Author: fantasai

css-scrollbars-1/Overview.bs

@@ -80,7 +80,7 @@ Value Definitions</h3>
 
 <pre class="propdef">
 Name: scrollbar-color
-Value: auto | dark | light | <<color>>{2}
+Value: auto | <<color>>{2}
 Initial: auto
 Inherited: yes
 Computed value: specified keyword or two computed colors
@@ -99,18 +99,6 @@ scrollbar-color value set on the HTML body element are not propagated to the vie
 <dl dfn-type="value" dfn-for="scrollbar-color">
 <dt><dfn>auto</dfn></dt>
 <dd>default platform rendering for the scrollbar.</dd>
-<dt><dfn>dark</dfn></dt>
-<dd>
-show a dark scrollbar,
-which can be either a dark variant of scrollbar provided by the platform,
-or a custom scrollbar with dark colors.
-</dd>
-<dt><dfn>light</dfn></dt>
-<dd>
-show a light scrollbar,
-which can be either a light variant of scrollbar provided by the platform,
-or a custom scrollbar with light colors.
-</dd>
 <dt><dfn><<color>></dfn></dt>
 <dd>
 apply the first color to the thumb of the scrollbar,
@@ -142,11 +130,6 @@ if the corresponding part do not exist on the underlying platform.
 When using 'scrollbar-color' property with specific color values,
 authors should ensure the specified colors have enough contrast between them.
 For keyword values, UAs should ensure the colors they use have enough contrast.
-UAs should ensure that their actual color values for 
-''scrollbar-color/light'' and ''scrollbar-color/dark'' 
-should provide sufficient contrast with the element’s background
-(i.e. ''scrollbar-color/light'' on a light background and ''scrollbar-color/dark'' on a dark background 
-should always have sufficient contrast)
 See 
 <a href="https://www.w3.org/TR/WCAG21/#non-text-contrast">WCAG 2.1 SC 1.4.11 Non-text Contrast</a> 
 [[WCAG21]]. 
@@ -256,6 +239,10 @@ This appendix is <em>informative</em>.
 This appendix describes changes from the
 <a href="https://www.w3.org/TR/2018/WD-css-scrollbars-1-20180925/">First Public Working Draft (FPWD) of 25 Sep 2018</a>.
 <ul>
+<li><a href="https://github.com/w3c/csswg-drafts/issues/6438">#6538</a>:
+    removed <css>light</css> and <css>dark</css> values of 'scrollbar-color'
+    in favor of allowing the UA to tune ''scrollbar-color/auto''
+    in accordance with 'color-scheme' or other contextual information.
 <li><a href="https://github.com/w3c/csswg-drafts/issues/3237">#3237</a>: 
     scrollbar-color computed value changed to: specified keyword or two computed colors
 </li>