[css-regions-1] Fix urls consistently (w3c#13363)

Author: alkorlos

css-regions-1/Overview.bs

@@ -571,7 +571,7 @@ The 'flow-from' property</h3>
 		Name: flow-from
 		Value: <<custom-ident>> | none
 		Initial: none
-		Applies To: Non-replaced <a href="https://www.w3.org/TR/CSS21/visuren.html#block-boxes">block containers</a>. <br/> This might be expanded in future versions of the specification to allow other types of containers to receive flow content.
+		Applies To: Non-replaced <a href="https://www.w3.org/TR/CSS2/visuren.html#block-boxes">block containers</a>. <br/> This might be expanded in future versions of the specification to allow other types of containers to receive flow content.
 		Inherited: no
 		Computed Value: as specified
 		Animation type: not animatable
@@ -595,7 +595,7 @@ The 'flow-from' property</h3>
 			<<custom-ident>>
 			name will be <a href="#region-flow-break">broken
 			into fragments</a> and visually formatted in the
-			<a href="https://www.w3.org/TR/CSS21/visuren.html#principal-box">principal boxes</a>
+			<a href="https://www.w3.org/TR/CSS2/visuren.html#principal-box">principal boxes</a>
 			of the <span>regions</span>
 			in the <a>region chain</a>.
 
@@ -870,7 +870,7 @@ The region-fragment property</h3>
 			Content flows as it would in a regular content box.
 			If the content exceeds the container box,
 			it is subject to the
-			<a href= "https://www.w3.org/TR/CSS21/visufx.html#propdef-overflow">overflow</a>
+			<a href= "https://www.w3.org/TR/CSS2/visufx.html#propdef-overflow">overflow</a>
 			property's computed value on the <a>CSS Region</a>.
 			Region breaks must be ignored on the <a>last usable region</a>.
 		</dd>
@@ -1197,7 +1197,7 @@ The Region mixin</h3>
 			<a>region chain</a> and
 			not able to fit the remaining content from the <a>named flow</a>.
 			Note that the region's
-			<a href= "https://www.w3.org/TR/CSS21/visufx.html#overflow">
+			<a href= "https://www.w3.org/TR/CSS2/visufx.html#overflow">
 				<code class= "idl">overflow</code></a>
 			property value can be used to control the
 			visibility of the overflowing content and the
@@ -1613,10 +1613,10 @@ The Region Flow Content Box (RFCB)</h3>
 	as for any other <a href="https://www.w3.org/TR/CSS2/visuren.html#block-boxes">block container box</a>.
 
 	The <span>RFCB</span> is a
-	<a href="https://www.w3.org/TR/CSS21/visuren.html#block-boxes">block container box</a>
+	<a href="https://www.w3.org/TR/CSS2/visuren.html#block-boxes">block container box</a>
 	with a computed 'width' of ''width/auto'' and whose used 'height' is resolved as detailed below.
 
-	Since the <span>RFCB</span> is a <a href="https://www.w3.org/TR/CSS21/visuren.html#block-boxes">block container box</a>, the ::before box and ::after box will also be block containers, though the contents of ::before and ::after may be inline within those boxes.
+	Since the <span>RFCB</span> is a <a href="https://www.w3.org/TR/CSS2/visuren.html#block-boxes">block container box</a>, the ::before box and ::after box will also be block containers, though the contents of ::before and ::after may be inline within those boxes.
 
 <h4 id="rfcb-width-resolution">
 RFCB 'width' resolution</h4>