[css-syntax-3] Update URLs to WHATWG specs

Author: xfq

css-syntax-3/Overview.bs

@@ -290,7 +290,7 @@ The input byte stream</h3>
 	If so, the user agent must decode these bytes into <a>code points</a> according to a particular character encoding.
 
 	To decode the stream of bytes into a stream of <a>code points</a>,
-	UAs must use the <dfn><a href="http://encoding.spec.whatwg.org/#decode">decode</a></dfn> algorithm
+	UAs must use the <dfn><a href="https://encoding.spec.whatwg.org/#decode">decode</a></dfn> algorithm
 	defined in [[!ENCODING]],
 	with the fallback encoding determined as follows.
 
@@ -303,7 +303,7 @@ The input byte stream</h3>
 	<ol>
 		<li>
 			If HTTP or equivalent protocol defines an encoding (e.g. via the charset parameter of the Content-Type header),
-			<dfn export><a href="http://encoding.spec.whatwg.org/#concept-encoding-get">get an encoding</a></dfn> [[!ENCODING]]
+			<dfn export><a href="https://encoding.spec.whatwg.org/#concept-encoding-get">get an encoding</a></dfn> [[!ENCODING]]
 			for the specified value.
 			If that does not return failure,
 			use the return value as the fallback encoding.
@@ -393,7 +393,7 @@ The input byte stream</h3>
 	New formats and new linking mechanisms <b>should not</b> provide an <a>environment encoding</a>,
 	so the stylesheet defaults to UTF-8 instead in the absence of more explicit information.
 
-	Note: [[HTML]] defines <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/links.html#link-type-stylesheet">the environment encoding for <code>&lt;link rel=stylesheet></code></a>.
+	Note: [[HTML]] defines <a href="https://html.spec.whatwg.org/multipage/links.html#link-type-stylesheet">the environment encoding for <code>&lt;link rel=stylesheet></code></a>.
 
 	Note: [[CSSOM]] defines <a href="https://drafts.csswg.org/cssom/#requirements-on-user-agents-implementing-the-xml-stylesheet-processing-instruction">the environment encoding for <code>&lt;xml-stylesheet?></code></a>.