[css-values] Fix grammar, export term.

Author: fantasai

css-values-3/Overview.bs

@@ -793,11 +793,12 @@ Percentages: the <<percentage>> type</h3>
 <h3 id='dimensions'>
 Numbers with Units: <a>dimensions</a></h3>
 
-	The general term "dimension" refers to a number with a unit attached to it,
-	and are denoted by <dfn>&lt;dimension></dfn>.
+	The general term <dfn export>dimension</dfn> refers to
+	a number with a unit attached to it;
+	and is denoted by <dfn>&lt;dimension></dfn>.
 
 	When written literally,
-	a <dfn>dimension</dfn> is a <a>number</a>
+	a <a>dimension</a> is a <a>number</a>
 	immediately followed by a unit identifier,
 	which is an <a>identifier</a>.
 	It corresponds to the <<dimension-token>> production

css-values-4/Overview.bs

@@ -789,11 +789,12 @@ Percentages: the <<percentage>> type</h3>
 <h3 id='dimensions'>
 Numbers with Units: <a>dimensions</a></h3>
 
-	The general term "dimension" refers to a number with a unit attached to it,
-	and are denoted by <dfn>&lt;dimension></dfn>.
+	The general term <dfn export>dimension</dfn> refers to
+	a number with a unit attached to it;
+	and is denoted by <dfn>&lt;dimension></dfn>.
 
 	When written literally,
-	a <dfn>dimension</dfn> is a <a>number</a>
+	a <a>dimension</a> is a <a>number</a>
 	immediately followed by a unit identifier,
 	which is an <a>identifier</a>.
 	It corresponds to the <<dimension-token>> production