[css-sizing-3] Fix IDs.

Author: fantasai

css-sizing-3/Overview.bs

@@ -303,7 +303,7 @@ Preferred Size Properties: the 'width and 'height' properties</h4>
 	The 'width' and 'height' properties specify
 	the preferred (<a>physical</a>) <dfn>width</dfn> and <dfn>height</dfn> of the box, respectively.
 
-<h4 id="preferred-size-properties">
+<h4 id="min-size-properties">
 Minimum Size Properties: the 'min-width and 'min-height' properties</h4>
 
 	<pre class=propdef>
@@ -325,7 +325,7 @@ Minimum Size Properties: the 'min-width and 'min-height' properties</h4>
 	Note: The initial value of ''min-width/auto'' is new;
 	in [[CSS2]] the initial value was zero.
 
-<h4 id="preferred-size-properties">
+<h4 id="max-size-properties">
 Maximum Size Properties: the 'max-width and 'max-height' properties</h4>
 
 	<pre class=propdef>