style: Don't use attribute selectors for determining if a select is a drop down or a list box.

Instead add a pseudo-class that does the expected size="" attribute parsing.

Removing the Gtk-specific rule setting the text color since it doesn't
seem to have any effect currently.

Differential Revision: https://phabricator.services.mozilla.com/D83448

components/style/invalidation/element/element_wrapper.rs

@@ -239,6 +239,15 @@ where
                 }
             },
 
+            #[cfg(feature = "gecko")]
+            NonTSPseudoClass::MozSelectListBox => {
+                if let Some(snapshot) = self.snapshot() {
+                    if snapshot.has_other_pseudo_class_state() {
+                        return snapshot.mIsSelectListBox();
+                    }
+                }
+            },
+
             // :lang() needs to match using the closest ancestor xml:lang="" or
             // lang="" attribtue from snapshots.
             NonTSPseudoClass::Lang(ref lang_arg) => {