[css-page-floats] minor syntax fix

Author: johanneswilm

css-page-floats/Overview.bs

@@ -73,7 +73,8 @@ Terminology</h2>
     <dt><dfn>Float reference</dfn>
     <dd>
       The entity to which the float is aligned.
-    <dt><dfn>Not overlapping</dfn></dt>
+    <dt><dfn>Not overlapping</dfn>
+    <dd>
       Two elements are not overlapping if the margin box of one element is not
       overlapping the margin box of the other element.
   </dl>