Update CSS Overflow reference to version we need

The HTML spec depends on having a CSS Overflow spec that defines the CSS
‘overflow’ property, but the spec at https://drafts.csswg.org/css-overflow/
no longer defines the ‘overflow’ property; instead, the ‘overflow’ property
definition is in the spec at https://drafts.csswg.org/css-overflow-3/. So, for
the time being at least, we have the HTML spec reference use that version
(the Level 3 version) of the CSS Overflow spec.

This change also drops *‘Level N’* qualifiers from a couple other CSS spec
names in the References section — because, regardless of what version of a
particular CSS module spec we’re referencing, our style is to consistently just
cite the name of the spec without the *‘Level N’* qualifier.

source

@@ -3558,9 +3558,9 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
     spec=CSSLISTS></p>
 
     <p>The <dfn
-    data-x-href="https://drafts.csswg.org/css-overflow/#propdef-overflow">'overflow'</dfn> property
+    data-x-href="https://drafts.csswg.org/css-overflow-3/#propdef-overflow">'overflow'</dfn> property
     and its <dfn
-    data-x-href="https://drafts.csswg.org/css-overflow/#valdef-overflow-hidden">'hidden'</dfn> value
+    data-x-href="https://drafts.csswg.org/css-overflow-3/#valdef-overflow-hidden">'hidden'</dfn> value
     are defined in the <cite>CSS Overflow</cite> specification. <ref spec=CSSOVERFLOW></p>
 
     <p>The following features are defined in the <cite>CSS Positioned Layout</cite> specification:
@@ -119426,10 +119426,10 @@ INSERT INTERFACES HERE
    <dd><cite><a href="https://drafts.csswg.org/css-backgrounds/">CSS Backgrounds and Borders </a></cite>, B. Bos, E. Etemad, B. Kemper. W3C.</dd>
 
    <dt id="refsCSSCASCADE">[CSSCASCADE]</dt>
-   <dd><cite><a href="https://drafts.csswg.org/css-cascade/">CSS Cascading and Inheritance Level 4</a></cite>, E. Etemad, T. Atkins. W3C.</dd>
+   <dd><cite><a href="https://drafts.csswg.org/css-cascade/">CSS Cascading and Inheritance</a></cite>, E. Etemad, T. Atkins. W3C.</dd>
 
    <dt id="refsCSSCOLOR">[CSSCOLOR]</dt>
-   <dd><cite><a href="https://drafts.csswg.org/css-color/">CSS Color Module Level 3</a></cite>, T. &Ccedil;elik, C. Lilley, L. Baron. W3C.</dd>
+   <dd><cite><a href="https://drafts.csswg.org/css-color/">CSS Color Module</a></cite>, T. &Ccedil;elik, C. Lilley, L. Baron. W3C.</dd>
 
    <dt id="refsCSSDISPLAY">[CSSDISPLAY]</dt>
    <dd><cite><a href="https://drafts.csswg.org/css-font-loading/">CSS Display</a></cite>, T. Atkins, E. Etemad. W3C.</dd>
@@ -119459,7 +119459,7 @@ INSERT INTERFACES HERE
    <dd><cite><a href="https://drafts.csswg.org/cssom-view/">CSSOM View Module</a></cite>, S. Pieters, G. Adams. W3C.</dd>
 
    <dt id="refsCSSOVERFLOW">[CSSOVERFLOW]</dt>
-   <dd><cite><a href="https://drafts.csswg.org/css-overflow/">CSS Overflow</a></cite>, L. Baron, F. Rivoal. W3C.</dd>
+   <dd><cite><a href="https://drafts.csswg.org/css-overflow-3">CSS Overflow Module</a></cite>, L. Baron, F. Rivoal. W3C.</dd>
 
    <dt id="refsCSSPOSITION">[CSSPOSITION]</dt>
    <dd><cite><a href="https://drafts.csswg.org/css-position/">CSS Positioned Layout</a></cite>, R. Atanassov, A. Eicholz. W3C.</dd>