[css2] Typo fix

Author: xfq

css2/visufx.html

@@ -73,7 +73,7 @@ <h2>11.1 <a name="overflow-clipping">Overflow and clipping</a></h2>
 absolutely</a>, partly outside the box.  Such boxes are not always
 clipped by the overflow property on their ancestors; specifically,
 they are not clipped by the overflow of any ancestor between
-themselves and their containing block
+themselves and their containing block.
 </li>
 <li>A descendant box has <a href="box.html#margin-properties">negative margins</a>, causing it
 to be positioned partly outside the box.

css2/visufx.src

@@ -42,7 +42,7 @@ height).
 absolutely</a>, partly outside the box.  Such boxes are not always
 clipped by the overflow property on their ancestors; specifically,
 they are not clipped by the overflow of any ancestor between
-themselves and their containing block
+themselves and their containing block.
 </li>
 <li>A descendant box has <a href="box.html#margin-properties">negative margins</a>, causing it
 to be positioned partly outside the box.