[css-overflow-5] Define that :disabled can match ::scroll-button(). w3c#11216

Author: tabatkins

css-overflow-5/Overview.bs

@@ -447,8 +447,19 @@ but maybe also <css>horizontal</css>/<css>vertical</css>/<css>block</css>/<css>i
 
 The ''::scroll-button()''s are [=fully stylable pseudo-elements=]: there is no restriction on what properties apply to them.
 
+The '':disabled'' pseudo-class can apply to ''::scroll-button()''.
+It matches a given button
+when their [=originating element=]
+can't be scrolled in their associated direction.
+
 Issue: The UA stylesheet needs to specify that ''::scroll-button()''s
-are styled identically to the <{button}> element.
+are styled identically to the <{button}> element,
+including disabled styles.
+
+Issue: Should ''::scroll-button()'' use the *full* UA styling of buttons,
+aka ''appearance:button''?
+Or the non-native rendering, aka ''appearance:none''?
+If the former, we'll obviously need to define the interaction with 'appearance'.
 
 
 <h3 id=focus-order>