[css-gcpm-3] Fix propdef block markup formatting (#4263)

Author: lahmatiy

css-gcpm-3/Overview.bs

@@ -438,7 +438,7 @@ The following new value of the 'float' property creates a footnote element:
 <pre class="propdef partial">
 	Name: float
 	New Values: footnote
-	</pre>
+</pre>
 <dl dfn-type="value" dfn-for="float">
 	<dt><dfn>footnote</dfn></dt>
 	<dd>each footnote element is placed in the footnote area of the page</dd>
@@ -454,7 +454,7 @@ The 'footnote-display' property determines whether a footnote is displayed as a
 	Inherited: no
 	Percentages: N/A
 	Computed value: specified value
-	</pre>
+</pre>
 
 
 <dl dfn-type="value" dfn-for="propdef-footnote-display">