LibWeb: Implement the <style> SVG element

The `<style>` element is allowed to be in the SVG namespace, so we now
support this element.

It has the same behaviour as the HTML namespace `<style>` element as
described in the spec.

"The semantics and processing of a ‘style’ and its attributes must be
the same as is defined for the HTML ‘style’ element."

Userland/Libraries/LibWeb/SVG/SVGStyleElement.cpp

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2023, Preston Taylor <PrestonLeeTaylor@proton.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/SVG/SVGStyleElement.h>
+
+namespace Web::SVG {
+
+SVGStyleElement::SVGStyleElement(DOM::Document& document, DOM::QualifiedName qualified_name)
+    : SVGElement(document, move(qualified_name))
+{
+}
+
+SVGStyleElement::~SVGStyleElement() = default;
+
+JS::ThrowCompletionOr<void> SVGStyleElement::initialize(JS::Realm& realm)
+{
+    MUST_OR_THROW_OOM(Base::initialize(realm));
+    set_prototype(&Bindings::ensure_web_prototype<Bindings::SVGStyleElementPrototype>(realm, "SVGStyleElement"));
+
+    return {};
+}
+
+void SVGStyleElement::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_style_element_utils.sheet());
+}
+
+void SVGStyleElement::children_changed()
+{
+    m_style_element_utils.update_a_style_block(*this);
+    Base::children_changed();
+}
+
+void SVGStyleElement::inserted()
+{
+    m_style_element_utils.update_a_style_block(*this);
+    Base::inserted();
+}
+
+void SVGStyleElement::removed_from(Node* old_parent)
+{
+    m_style_element_utils.update_a_style_block(*this);
+    Base::removed_from(old_parent);
+}
+
+// https://www.w3.org/TR/cssom/#dom-linkstyle-sheet
+CSS::CSSStyleSheet* SVGStyleElement::sheet()
+{
+    // The sheet attribute must return the associated CSS style sheet for the node or null if there is no associated CSS style sheet.
+    return m_style_element_utils.sheet();
+}
+
+// https://www.w3.org/TR/cssom/#dom-linkstyle-sheet
+CSS::CSSStyleSheet const* SVGStyleElement::sheet() const
+{
+    // The sheet attribute must return the associated CSS style sheet for the node or null if there is no associated CSS style sheet.
+    return m_style_element_utils.sheet();
+}
+
+}

Userland/Libraries/LibWeb/SVG/SVGStyleElement.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2023, Preston Taylor <PrestonLeeTaylor@proton.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/DOM/StyleElementUtils.h>
+#include <LibWeb/SVG/SVGElement.h>
+
+namespace Web::SVG {
+
+class SVGStyleElement final : public SVGElement {
+    WEB_PLATFORM_OBJECT(HTMLStyleElement, SVGElement);
+
+public:
+    virtual ~SVGStyleElement() override;
+
+    virtual void children_changed() override;
+    virtual void inserted() override;
+    virtual void removed_from(Node*) override;
+
+    CSS::CSSStyleSheet* sheet();
+    CSS::CSSStyleSheet const* sheet() const;
+
+private:
+    SVGStyleElement(DOM::Document&, DOM::QualifiedName);
+
+    virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    // The semantics and processing of a ‘style’ and its attributes must be the same as is defined for the HTML ‘style’ element.
+    DOM::StyleElementUtils m_style_element_utils;
+};
+
+}

Userland/Libraries/LibWeb/SVG/SVGStyleElement.idl

@@ -0,0 +1,11 @@
+#import <CSS/LinkStyle.idl>
+#import <SVG/SVGElement.idl>
+
+[Exposed=Window]
+interface SVGStyleElement : SVGElement {
+  [Reflect] attribute DOMString type;
+  [Reflect] attribute DOMString media;
+  [Reflect] attribute DOMString title;
+};
+
+SVGStyleElement includes LinkStyle;

Userland/Libraries/LibWeb/SVG/TagNames.h

@@ -33,6 +33,7 @@ namespace Web::SVG::TagNames {
     __ENUMERATE_SVG_TAG(radialGradient) \
     __ENUMERATE_SVG_TAG(script)         \
     __ENUMERATE_SVG_TAG(stop)           \
+    __ENUMERATE_SVG_TAG(style)          \
     __ENUMERATE_SVG_TAG(symbol)         \
     __ENUMERATE_SVG_TAG(title)          \
     __ENUMERATE_SVG_TAG(use)