diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index 01f93439e3..26412944fa 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -596,11 +596,6 @@ Page const* Window::page() const
     return associated_document().page();
 }
 
-CSS::CSSStyleDeclaration* Window::get_computed_style_impl(DOM::Element& element) const
-{
-    return CSS::ResolvedCSSStyleDeclaration::create(element).release_value_but_fixme_should_propagate_errors().ptr();
-}
-
 Optional<CSS::MediaFeatureValue> Window::query_media_feature(CSS::MediaFeatureID media_feature) const
 {
     // FIXME: Many of these should be dependent on the hardware
@@ -964,7 +959,6 @@ WebIDL::ExceptionOr<void> Window::initialize_web_interfaces(Badge<WindowEnvironm
     define_native_function(realm, "requestIdleCallback", request_idle_callback, 1, attr);
     define_native_function(realm, "cancelIdleCallback", cancel_idle_callback, 1, attr);
 
-    define_native_function(realm, "getComputedStyle", get_computed_style, 1, attr);
     define_native_function(realm, "getSelection", get_selection, 0, attr);
 
     define_native_function(realm, "structuredClone", structured_clone, 1, attr);
@@ -1213,6 +1207,14 @@ Variant<JS::Handle<DOM::Event>, JS::Value> Window::event() const
     return JS::js_undefined();
 }
 
+// https://w3c.github.io/csswg-drafts/cssom/#dom-window-getcomputedstyle
+WebIDL::ExceptionOr<JS::NonnullGCPtr<CSS::CSSStyleDeclaration>> Window::get_computed_style(DOM::Element& element, Optional<String> const& pseudo_element) const
+{
+    // FIXME: Make this fully spec compliant.
+    (void)pseudo_element;
+    return MUST_OR_THROW_OOM(heap().allocate<CSS::ResolvedCSSStyleDeclaration>(realm(), element));
+}
+
 // https://w3c.github.io/csswg-drafts/cssom-view/#dom-window-matchmedia
 WebIDL::ExceptionOr<JS::NonnullGCPtr<CSS::MediaQueryList>> Window::match_media(String const& query)
 {
@@ -1654,16 +1656,6 @@ JS_DEFINE_NATIVE_FUNCTION(Window::location_setter)
     return JS::js_undefined();
 }
 
-JS_DEFINE_NATIVE_FUNCTION(Window::get_computed_style)
-{
-    auto* impl = TRY(impl_from(vm));
-    auto* object = TRY(vm.argument(0).to_object(vm));
-    if (!is<DOM::Element>(object))
-        return vm.throw_completion<JS::TypeError>(JS::ErrorType::NotAnObjectOfType, "DOM element");
-
-    return impl->get_computed_style_impl(*static_cast<DOM::Element*>(object));
-}
-
 // https://w3c.github.io/selection-api/#dom-window-getselection
 JS_DEFINE_NATIVE_FUNCTION(Window::get_selection)
 {
diff --git a/Userland/Libraries/LibWeb/HTML/Window.h b/Userland/Libraries/LibWeb/HTML/Window.h
index 099e2880ff..b95a6ef520 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.h
+++ b/Userland/Libraries/LibWeb/HTML/Window.h
@@ -108,7 +108,6 @@ public:
     DOM::Event const* current_event() const { return m_current_event.ptr(); }
     void set_current_event(DOM::Event* event);
 
-    CSS::CSSStyleDeclaration* get_computed_style_impl(DOM::Element&) const;
     Optional<CSS::MediaFeatureValue> query_media_feature(CSS::MediaFeatureID) const;
 
     void fire_a_page_transition_event(DeprecatedFlyString const& event_name, bool persisted);
@@ -159,6 +158,8 @@ public:
 
     Variant<JS::Handle<DOM::Event>, JS::Value> event() const;
 
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<CSS::CSSStyleDeclaration>> get_computed_style(DOM::Element&, Optional<String> const& pseudo_element) const;
+
     WebIDL::ExceptionOr<JS::NonnullGCPtr<CSS::MediaQueryList>> match_media(String const& query);
     WebIDL::ExceptionOr<JS::NonnullGCPtr<CSS::Screen>> screen();
 
@@ -257,7 +258,6 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(cancel_animation_frame);
     JS_DECLARE_NATIVE_FUNCTION(focus);
 
-    JS_DECLARE_NATIVE_FUNCTION(get_computed_style);
     JS_DECLARE_NATIVE_FUNCTION(get_selection);
 
     JS_DECLARE_NATIVE_FUNCTION(queue_microtask);
diff --git a/Userland/Libraries/LibWeb/HTML/Window.idl b/Userland/Libraries/LibWeb/HTML/Window.idl
index f695736078..5dcef66cfc 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.idl
+++ b/Userland/Libraries/LibWeb/HTML/Window.idl
@@ -44,6 +44,9 @@ interface Window : EventTarget {
     // https://dom.spec.whatwg.org/#interface-window-extensions
     [Replaceable] readonly attribute (Event or undefined) event; // legacy
 
+    // https://w3c.github.io/csswg-drafts/cssom/#extensions-to-the-window-interface
+    [NewObject] CSSStyleDeclaration getComputedStyle(Element elt, optional CSSOMString? pseudoElt);
+
     // https://w3c.github.io/csswg-drafts/cssom-view/#extensions-to-the-window-interface
     [NewObject] MediaQueryList matchMedia(CSSOMString query);
     [SameObject, Replaceable] readonly attribute Screen screen;