[css-color-adjust-1] Move color-scheme meta to HTML

Per resolution in issue #3846. Add a reference to the HTML specification
from the specification of the color-scheme property.

HTML pull request: whatwg/html#5938

Author: lilles

css-color-adjust-1/Overview.bs

@@ -218,6 +218,10 @@ Opting Into a Preferred Color Scheme: the 'color-scheme' property {#color-scheme
 		affects what <<system-color>>s resolve to.
 	</div>
 
+	[[HTML]] specifies a <a href="https://html.spec.whatwg.org/multipage/semantics.html#meta-color-scheme">color-scheme</a>
+	<{meta}> tag which can be used to set the color-scheme on the root element as
+	a [[css-cascade-4#preshint|non-CSS presentational hint]].
+
 	Note: “Light” and “dark” color schemes are not specific color palettes.
 	For example,
 	both a stark black-on-white scheme and a sepia dark-on-tan scheme
@@ -260,47 +264,6 @@ Effects of the Used Color Scheme {#color-scheme-effect}
 	via elements intended for graphics
 	(such as <{img}> elements embedding an SVG document).
 
-The "color-scheme" <{meta}> value {#color-scheme-meta}
----------------------------------
-
-	To aid user agents in rendering the page background with the desired [=color scheme=] immediately
-	(rather than waiting for all CSS in the page to load),
-	a 'color-scheme' value can also be provided in a <{meta}> element.
-
-	If any <{meta}> elements are [=inserted into a document=] or [=removed from a document=],
-	or existing <{meta}> elements have their <{meta/name}> or <{meta/content}> attributes changed,
-	user agents must run the following algorithm:
-
-	<div algorithm="find the color-scheme meta">
-		1. Let |candidate elements| be the list of all <{meta}> elements that meet the following criteria,
-			in [=tree order=]:
-
-			* the element is [=in a document tree=]
-			* the element has a <{meta/name}> attribute,
-				whose value is an [=ASCII case-insensitive=] match for <code>color-scheme</code>
-			* the element has a <{meta/content}> attribute,
-				whose value is not the empty string
-			* the element is a child of the [=the head element=] of the document
-
-		2. For each |element| in |candidate elements|:
-			1. If |element|’s <{meta/content}> attribute's value
-				[=CSS/parses=] as a <'color-scheme'> value,
-				treat that value as a declaration of the 'color-scheme' property on |element|’s [=tree/root=],
-				cascaded as a [[css-cascade-4#preshint|non-CSS presentational hint]].
-				Then return.
-
-		Note: Because these rules check successive elements until they find a match,
-		an author can provide multiple such values
-		to handle fallback for legacy user agents.
-		Opposite how CSS fallback works for properties,
-		the multiple <{meta}> elements must be arranged
-		with the legacy values <em>after</em> the newer values.
-	</div>
-
-	Issue(#3846): This algorithm favors the first <{meta}>,
-	to allow for ASAP rendering with a chosen color scheme.
-	Is that the desired behavior?
-
 
 Forced Color Schemes: the 'forced-color-adjust' property {#forced}
 ====================