[css-conditional-5] Add axis keywords for overflowing #11183 (#11295)

Co-authored-by: Rune Lillesveen <futhark@google.com>

Author: lilles

css-conditional-5/Overview.bs

@@ -1489,7 +1489,7 @@ Scrollable: the '@container/scrollable' feature</h4>
 	<pre class="descdef mq">
 		Name: scrollable
 		For: @container
-		Value: none | top | right | bottom | left | block-start | inline-start | block-end | inline-end
+		Value: none | top | right | bottom | left | block-start | inline-start | block-end | inline-end | x | y | block | inline
 		Type: discrete
 	</pre>
 
@@ -1531,6 +1531,18 @@ Scrollable: the '@container/scrollable' feature</h4>
 		<dt><dfn>inline-end</dfn>
 		<dd>
 			The [=scroll container=] has [=scrollable overflow=] past the [=inline-end=] edge.
+		<dt><dfn>x</dfn>
+		<dd>
+			The [=scroll container=] has horizontally [=scrollable overflow=].
+		<dt><dfn>y</dfn>
+		<dd>
+			The [=scroll container=] has vertically [=scrollable overflow=].
+		<dt><dfn>block</dfn>
+		<dd>
+			The [=scroll container=] has [=scrollable overflow=] in its block direction.
+		<dt><dfn>inline</dfn>
+		<dd>
+			The [=scroll container=] has [=scrollable overflow=] in its inline direction.
 	</dl>