[css-position-3] Shift dfn higher in the section

Author: fantasai

css-position-3/Overview.bs

@@ -731,6 +731,7 @@ Absolute (and Fixed) Positioning</h3>
 	the [=inset properties=] effectively reduce the [=containing block=]
 	into which it is sized and positioned
 	by the specified amounts.
+	The resulting rectangle is called the <dfn>inset-modified containing block</dfn>.
 
 	If only one [=inset property=] in a given axis is ''top/auto'',
 	it is set to zero.
@@ -783,7 +784,7 @@ Absolute (and Fixed) Positioning</h3>
 	(where [=end=] is interpreted relative to the [=writing mode=] of the [=containing block=]).
 
 	Note: Sizing and positioning of the [=absolutely positioned box=]
-	into this <dfn>inset-modified containing block</dfn>
+	into this [=inset-modified containing block=]
 	is as described in [[#abspos-layout]].
 
 	If its [=self-alignment property=] in an axis is ''align-self/normal'',