[css-flexbox] Fix links.

Author: fantasai

css-flexbox/Overview.bs

@@ -1746,18 +1746,18 @@ Alignment</h2>
 
 	<p>
 		The 'margin' properties can be used to align items in a manner similar to, but more powerful than, what margins can do in block layout.
-		<i>Flex items</i> also respect the alignment properties from the Box Alignment spec,
+		<i>Flex items</i> also respect the alignment properties from <a href="http://www.w3.org/TR/css-align/">CSS Box Alignment</a>,
 		which allow easy keyword-based alignment of items in both the <i>main axis</i> and <i>cross axis</i>.
 		These properties make many common types of alignment trivial,
 		including some things that were very difficult in CSS 2.1,
 		like horizontal and vertical centering.
 
 	<p class='note'>
-		While the alignment properties are defined in the Box Alignment spec,
+		While the alignment properties are defined in <a href="http://www.w3.org/TR/css-align/">CSS Box Alignment</a>,
 		Flexible Box Layout reproduces the definitions of the relevant ones here
 		so as to not create a normative dependency that may slow down advancement of the spec.
 		These properties apply only to flex layout
-		until Box Alignment is finished
+		until <a href="http://www.w3.org/TR/css-align-3/">CSS Box Alignment Level 3</a> is finished
 		and defines their effect for other layout modes.
 
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