diff --git a/Libraries/LibWeb/CMakeLists.txt b/Libraries/LibWeb/CMakeLists.txt
index 67d9ff8df2a..5c1d1f1c7fb 100644
--- a/Libraries/LibWeb/CMakeLists.txt
+++ b/Libraries/LibWeb/CMakeLists.txt
@@ -186,6 +186,7 @@ set(SOURCES
     CSS/StyleInvalidation.cpp
     CSS/StyleInvalidationData.cpp
     CSS/StyleProperty.cpp
+    CSS/StylePropertyMapReadOnly.cpp
     CSS/StyleSheet.cpp
     CSS/StyleSheetIdentifier.cpp
     CSS/StyleSheetList.cpp
diff --git a/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.cpp b/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.cpp
new file mode 100644
index 00000000000..8e2291fcc14
--- /dev/null
+++ b/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.cpp
@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "StylePropertyMapReadOnly.h"
+#include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/Bindings/StylePropertyMapReadOnlyPrototype.h>
+#include <LibWeb/CSS/CSSStyleDeclaration.h>
+#include <LibWeb/CSS/PropertyName.h>
+#include <LibWeb/WebIDL/ExceptionOr.h>
+
+namespace Web::CSS {
+
+GC_DEFINE_ALLOCATOR(StylePropertyMapReadOnly);
+
+GC::Ref<StylePropertyMapReadOnly> StylePropertyMapReadOnly::create_computed_style(JS::Realm& realm, DOM::AbstractElement element)
+{
+    return realm.create<StylePropertyMapReadOnly>(realm, element);
+}
+
+StylePropertyMapReadOnly::StylePropertyMapReadOnly(JS::Realm& realm, Optional<DOM::AbstractElement> element)
+    : Bindings::PlatformObject(realm)
+    , m_source_element(move(element))
+{
+}
+
+StylePropertyMapReadOnly::StylePropertyMapReadOnly(JS::Realm& realm, GC::Ref<CSSStyleDeclaration> declaration)
+    : Bindings::PlatformObject(realm)
+    , m_source_declaration(declaration)
+{
+}
+
+StylePropertyMapReadOnly::~StylePropertyMapReadOnly() = default;
+
+void StylePropertyMapReadOnly::initialize(JS::Realm& realm)
+{
+    WEB_SET_PROTOTYPE_FOR_INTERFACE(StylePropertyMapReadOnly);
+    Base::initialize(realm);
+}
+
+void StylePropertyMapReadOnly::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+
+    visitor.visit(m_source_declaration);
+    if (m_source_element.has_value())
+        m_source_element->visit(visitor);
+}
+
+// https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-get
+WebIDL::ExceptionOr<Variant<GC::Ref<CSSStyleValue>, Empty>> StylePropertyMapReadOnly::get(String property)
+{
+    // The get(property) method, when called on a StylePropertyMapReadOnly this, must perform the following steps:
+
+    // 1. If property is not a custom property name string, set property to property ASCII lowercased.
+    if (!is_a_custom_property_name_string(property))
+        property = property.to_ascii_lowercase();
+
+    // 2. If property is not a valid CSS property, throw a TypeError.
+    if (!is_a_valid_css_property(property))
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("'{}' is not a valid CSS property", property)) };
+
+    // 3. Let props be the value of this’s [[declarations]] internal slot.
+    auto& props = m_declarations;
+
+    // FIXME: 4. If props[property] exists, subdivide into iterations props[property], then reify the first item of the result and return it.
+    (void)props;
+
+    // 5. Otherwise, return undefined.
+    return Empty {};
+}
+
+// https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-getall
+WebIDL::ExceptionOr<Vector<GC::Ref<CSSStyleValue>>> StylePropertyMapReadOnly::get_all(String property)
+{
+    // The getAll(property) method, when called on a StylePropertyMap this, must perform the following steps:
+
+    // 1. If property is not a custom property name string, set property to property ASCII lowercased.
+    if (!is_a_custom_property_name_string(property))
+        property = property.to_ascii_lowercase();
+
+    // 2. If property is not a valid CSS property, throw a TypeError.
+    if (!is_a_valid_css_property(property))
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("'{}' is not a valid CSS property", property)) };
+
+    // 3. Let props be the value of this’s [[declarations]] internal slot.
+    auto& props = m_declarations;
+
+    // FIXME: 4. If props[property] exists, subdivide into iterations props[property], then reify each item of the result, and return the list.
+    (void)props;
+
+    // 5. Otherwise, return an empty list.
+    return Vector<GC::Ref<CSSStyleValue>> {};
+}
+
+// https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-has
+WebIDL::ExceptionOr<bool> StylePropertyMapReadOnly::has(String property)
+{
+    // The has(property) method, when called on a StylePropertyMapReadOnly this, must perform the following steps:
+
+    // 1. If property is not a custom property name string, set property to property ASCII lowercased.
+    if (!is_a_custom_property_name_string(property))
+        property = property.to_ascii_lowercase();
+
+    // 2. If property is not a valid CSS property, throw a TypeError.
+    if (!is_a_valid_css_property(property))
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("'{}' is not a valid CSS property", property)) };
+
+    // 3. Let props be the value of this’s [[declarations]] internal slot.
+    auto& props = m_declarations;
+
+    // 4. If props[property] exists, return true. Otherwise, return false.
+    return props.contains(property);
+}
+
+// https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-size
+WebIDL::UnsignedLong StylePropertyMapReadOnly::size() const
+{
+    // The size attribute, on getting from a StylePropertyMapReadOnly this, must perform the following steps:
+
+    // 1. Return the size of the value of this’s [[declarations]] internal slot.
+    return m_declarations.size();
+}
+
+}
diff --git a/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.h b/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.h
new file mode 100644
index 00000000000..8b0e5ab3041
--- /dev/null
+++ b/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2025, Sam Atkins <sam@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/CSS/StyleValues/StyleValue.h>
+#include <LibWeb/DOM/AbstractElement.h>
+#include <LibWeb/WebIDL/Types.h>
+
+namespace Web::CSS {
+
+// https://drafts.css-houdini.org/css-typed-om-1/#stylepropertymapreadonly
+class StylePropertyMapReadOnly : public Bindings::PlatformObject {
+    WEB_PLATFORM_OBJECT(StylePropertyMapReadOnly, Bindings::PlatformObject);
+    GC_DECLARE_ALLOCATOR(StylePropertyMapReadOnly);
+
+public:
+    [[nodiscard]] static GC::Ref<StylePropertyMapReadOnly> create_computed_style(JS::Realm&, DOM::AbstractElement);
+
+    virtual ~StylePropertyMapReadOnly() override;
+
+    WebIDL::ExceptionOr<Variant<GC::Ref<CSSStyleValue>, Empty>> get(String property);
+    WebIDL::ExceptionOr<Vector<GC::Ref<CSSStyleValue>>> get_all(String property);
+    WebIDL::ExceptionOr<bool> has(String property);
+    WebIDL::UnsignedLong size() const;
+
+protected:
+    explicit StylePropertyMapReadOnly(JS::Realm&, GC::Ref<CSSStyleDeclaration>);
+    explicit StylePropertyMapReadOnly(JS::Realm&, Optional<DOM::AbstractElement> = {});
+
+    virtual void initialize(JS::Realm&) override;
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    Optional<DOM::AbstractElement> m_source_element;
+    GC::Ptr<CSSStyleDeclaration> m_source_declaration;
+
+    // https://drafts.css-houdini.org/css-typed-om-1/#dom-stylepropertymapreadonly-declarations-slot
+    // A StylePropertyMapReadOnly object has a [[declarations]] internal slot, which is a map reflecting the CSS
+    // declaration block’s declarations.
+    HashMap<FlyString, NonnullRefPtr<StyleValue>> m_declarations;
+};
+
+}
diff --git a/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.idl b/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.idl
new file mode 100644
index 00000000000..4c43062edd7
--- /dev/null
+++ b/Libraries/LibWeb/CSS/StylePropertyMapReadOnly.idl
@@ -0,0 +1,12 @@
+#import <CSS/CSSStyleValue.idl>
+
+// https://drafts.css-houdini.org/css-typed-om-1/#stylepropertymapreadonly
+// FIXME: [Exposed=(Window, Worker, PaintWorklet, LayoutWorklet)]
+[Exposed=(Window, Worker)]
+interface StylePropertyMapReadOnly {
+    // FIXME: iterable<USVString, sequence<CSSStyleValue>>;
+    (undefined or CSSStyleValue) get(USVString property);
+    sequence<CSSStyleValue> getAll(USVString property);
+    boolean has(USVString property);
+    readonly attribute unsigned long size;
+};
diff --git a/Libraries/LibWeb/Forward.h b/Libraries/LibWeb/Forward.h
index 8ea7d73a871..04aa34d4be2 100644
--- a/Libraries/LibWeb/Forward.h
+++ b/Libraries/LibWeb/Forward.h
@@ -223,6 +223,7 @@ class ColorMixStyleValue;
 class ColorSchemeStyleValue;
 class ColorFunctionStyleValue;
 class ColorStyleValue;
+class ComputedProperties;
 class ConicGradientStyleValue;
 class ContentStyleValue;
 class CounterDefinitionsStyleValue;
@@ -336,7 +337,7 @@ class Size;
 class ScrollbarColorStyleValue;
 class StringStyleValue;
 class StyleComputer;
-class ComputedProperties;
+class StylePropertyMapReadOnly;
 class StyleSheet;
 class StyleSheetList;
 class StyleValue;
diff --git a/Libraries/LibWeb/idl_files.cmake b/Libraries/LibWeb/idl_files.cmake
index 00f778e254c..534111cb6e3 100644
--- a/Libraries/LibWeb/idl_files.cmake
+++ b/Libraries/LibWeb/idl_files.cmake
@@ -58,6 +58,7 @@ libweb_js_bindings(CSS/MediaQueryList)
 libweb_js_bindings(CSS/MediaQueryListEvent)
 libweb_js_bindings(CSS/Screen)
 libweb_js_bindings(CSS/ScreenOrientation)
+libweb_js_bindings(CSS/StylePropertyMapReadOnly)
 libweb_js_bindings(CSS/StyleSheet)
 libweb_js_bindings(CSS/StyleSheetList)
 libweb_js_bindings(CSS/TransitionEvent)
diff --git a/Tests/LibWeb/Text/expected/all-window-properties.txt b/Tests/LibWeb/Text/expected/all-window-properties.txt
index cda81dbfdba..a6b89b5da10 100644
--- a/Tests/LibWeb/Text/expected/all-window-properties.txt
+++ b/Tests/LibWeb/Text/expected/all-window-properties.txt
@@ -409,6 +409,7 @@ Storage
 StorageEvent
 StorageManager
 String
+StylePropertyMapReadOnly
 StyleSheet
 StyleSheetList
 SubmitEvent