LibWeb: Add handling for view transition selector specificity

The corresponding WPT test was not imported since it still fails
for unrelated reasons. As it stands right now, we have no way of
testing this behavior.

Author: Psychpsyo

Libraries/LibWeb/CSS/Selector.cpp

@@ -266,9 +266,14 @@ u32 Selector::specificity() const
                 ++tag_names;
                 break;
             case SimpleSelector::Type::PseudoElement:
-                // count the number of type selectors and pseudo-elements in the selector (= C)
-                // FIXME: This needs special handling for view transition pseudos:
-                //        https://drafts.csswg.org/css-view-transitions-1/#named-view-transition-pseudo
+                // https://drafts.csswg.org/css-view-transitions-1/#named-view-transition-pseudo
+                // The specificity of a named view transition pseudo-element selector with a <custom-ident> argument is equivalent
+                // to a type selector. The specificity of a named view transition pseudo-element selector with a '*' argument is zero.
+                // NB: We just break before adding to the type (tag name) specificity in case this is a named view transition pseudo that uses '*'
+                if (first_is_one_of(simple_selector.pseudo_element().type(), CSS::PseudoElement::ViewTransitionGroup, CSS::PseudoElement::ViewTransitionImagePair, CSS::PseudoElement::ViewTransitionOld, CSS::PseudoElement::ViewTransitionNew) && simple_selector.pseudo_element().pt_name_selector().is_universal)
+                    break;
+
+                // otherwise just count the number of type selectors and pseudo-elements in the selector (= C)
                 ++tag_names;
                 break;
             case SimpleSelector::Type::Universal: