diff --git a/AK/Optional.h b/AK/Optional.h
index 6342b7120e73..cd4694073007 100644
--- a/AK/Optional.h
+++ b/AK/Optional.h
@@ -9,7 +9,11 @@
 #pragma once
 
 #include <AK/Assertions.h>
+#include <AK/Concepts.h>
+#include <AK/Forward.h>
 #include <AK/Noncopyable.h>
+#include <AK/Platform.h>
+#include <AK/StdLibExtraDetails.h>
 #include <AK/StdLibExtras.h>
 #include <AK/Traits.h>
 #include <AK/Try.h>
@@ -33,10 +37,17 @@ struct ConditionallyResultType<false, T> {
     using Type = T;
 };
 
+template<typename Self, typename T>
+struct AddConstIfNeeded {
+    using Type = Conditional<IsConst<RemoveReference<Self>> && !IsConst<T>, AddConst<T>, T>;
+};
+
 }
 
 template<auto condition, typename T>
 using ConditionallyResultType = typename Detail::ConditionallyResultType<condition, T>::Type;
+template<typename Self, typename T>
+using AddConstIfNeeded = typename Detail::AddConstIfNeeded<Self, T>::Type;
 
 // NOTE: If you're here because of an internal compiler error in GCC 10.3.0+,
 //       it's because of the following bug:
@@ -53,116 +64,92 @@ struct OptionalNone {
     explicit constexpr OptionalNone() = default;
 };
 
-template<typename T, typename Self = Optional<T>>
-requires(!IsLvalueReference<Self>) class [[nodiscard]] OptionalBase {
+template<typename T>
+requires(!IsLvalueReference<T>)
+class [[nodiscard]] OptionalBase {
 public:
     using ValueType = T;
 
-    template<SameAs<OptionalNone> V>
-    ALWAYS_INLINE constexpr Self& operator=(V)
+    template<typename Self, SameAs<OptionalNone> V>
+    ALWAYS_INLINE constexpr Self& operator=(this Self& self, V)
     {
-        static_cast<Self&>(*this).clear();
-        return static_cast<Self&>(*this);
+        self.clear();
+        return self;
     }
 
-    [[nodiscard]] ALWAYS_INLINE constexpr T* ptr() &
+    template<typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr AddConstIfNeeded<Self, T>* ptr(this Self& self)
     {
-        return static_cast<Self&>(*this).has_value() ? __builtin_launder(reinterpret_cast<T*>(&static_cast<Self&>(*this).value())) : nullptr;
+        return self.has_value() ? &self.value() : nullptr;
     }
 
-    [[nodiscard]] ALWAYS_INLINE constexpr T const* ptr() const&
+    template<typename O = T, typename Fallback = O, typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr O value_or(this Self&& self, Fallback&& fallback)
     {
-        return static_cast<Self const&>(*this).has_value() ? __builtin_launder(reinterpret_cast<T const*>(&static_cast<Self const&>(*this).value())) : nullptr;
+        if (self.has_value())
+            return forward<Self>(self).value();
+        return forward<Fallback>(fallback);
     }
 
-    template<typename O = T, typename Fallback = O>
-    [[nodiscard]] ALWAYS_INLINE constexpr O value_or(Fallback const& fallback) const&
+    template<typename Callback, typename O = T, typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr O value_or_lazy_evaluated(this Self&& self, Callback callback)
     {
-        if (static_cast<Self const&>(*this).has_value())
-            return static_cast<Self const&>(*this).value();
-        return fallback;
-    }
-
-    template<typename O = T, typename Fallback = O>
-    requires(!IsLvalueReference<O> && !IsRvalueReference<O>)
-    [[nodiscard]] ALWAYS_INLINE constexpr O value_or(Fallback&& fallback) &&
-    {
-        if (static_cast<Self&>(*this).has_value())
-            return move(static_cast<Self&>(*this).value());
-        return move(fallback);
-    }
-
-    template<typename Callback, typename O = T>
-    [[nodiscard]] ALWAYS_INLINE constexpr O value_or_lazy_evaluated(Callback callback) const
-    {
-        if (static_cast<Self const&>(*this).has_value())
-            return static_cast<Self const&>(*this).value();
+        if (self.has_value())
+            return forward<Self>(self).value();
         return callback();
     }
 
-    template<typename Callback, typename O = T>
-    [[nodiscard]] ALWAYS_INLINE constexpr Optional<O> value_or_lazy_evaluated_optional(Callback callback) const
+    template<typename Callback, typename O = T, typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr Optional<O> value_or_lazy_evaluated_optional(this Self&& self, Callback callback)
     {
-        if (static_cast<Self const&>(*this).has_value())
-            return static_cast<Self const&>(*this).value();
+        if (self.has_value())
+            return forward<Self>(self);
         return callback();
     }
 
-    template<typename Callback, typename O = T>
-    [[nodiscard]] ALWAYS_INLINE constexpr ErrorOr<O> try_value_or_lazy_evaluated(Callback callback) const
+    template<typename Callback, typename O = T, typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr ErrorOr<O> try_value_or_lazy_evaluated(this Self&& self, Callback callback)
     {
-        if (static_cast<Self const&>(*this).has_value())
-            return static_cast<Self const&>(*this).value();
+        if (self.has_value())
+            return forward<Self>(self).value();
         return TRY(callback());
     }
 
-    template<typename Callback, typename O = T>
-    [[nodiscard]] ALWAYS_INLINE constexpr ErrorOr<Optional<O>> try_value_or_lazy_evaluated_optional(Callback callback) const
+    template<typename Callback, typename O = T, typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr ErrorOr<Optional<O>> try_value_or_lazy_evaluated_optional(this Self&& self, Callback callback)
     {
-        if (static_cast<Self const&>(*this).has_value())
-            return static_cast<Self const&>(*this).value();
+        if (self.has_value())
+            return forward<Self>(self);
         return TRY(callback());
     }
 
-    template<typename Callable>
-    [[nodiscard]] ALWAYS_INLINE constexpr T& ensure(Callable callable) &
+    template<typename Callable, typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr T& ensure(this Self& self, Callable callable)
     {
-        if (!static_cast<Self&>(*this).has_value())
-            static_cast<Self&>(*this) = callable();
-        return static_cast<Self&>(*this).value();
+        if (!self.has_value())
+            self = callable();
+        return self.value();
     }
 
-    [[nodiscard]] ALWAYS_INLINE constexpr T const& operator*() const { return static_cast<Self const&>(*this).value(); }
-    [[nodiscard]] ALWAYS_INLINE constexpr T& operator*() { return static_cast<Self&>(*this).value(); }
-
-    ALWAYS_INLINE constexpr T const* operator->() const { return &static_cast<Self const&>(*this).value(); }
-    ALWAYS_INLINE constexpr T* operator->() { return &static_cast<Self&>(*this).value(); }
+    template<typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr auto operator*(this Self&& self) -> decltype(forward<Self>(self).value()) { return forward<Self>(self).value(); }
+    template<typename Self>
+    [[nodiscard]] ALWAYS_INLINE constexpr AddConstIfNeeded<Self, T>* operator->(this Self&& self) { return &self.value(); }
 
-    template<typename F, typename MappedType = decltype(declval<F>()(declval<T&>())), auto IsErrorOr = IsSpecializationOf<MappedType, ErrorOr>, typename OptionalType = Optional<ConditionallyResultType<IsErrorOr, MappedType>>>
-    ALWAYS_INLINE constexpr Conditional<IsErrorOr, ErrorOr<OptionalType>, OptionalType> map(F&& mapper)
-    {
-        if constexpr (IsErrorOr) {
-            if (static_cast<Self&>(*this).has_value())
-                return OptionalType { TRY(mapper(static_cast<Self&>(*this).value())) };
-            return OptionalType {};
-        } else {
-            if (static_cast<Self&>(*this).has_value())
-                return OptionalType { mapper(static_cast<Self&>(*this).value()) };
-
-            return OptionalType {};
-        }
-    }
-
-    template<typename F, typename MappedType = decltype(declval<F>()(declval<T&>())), auto IsErrorOr = IsSpecializationOf<MappedType, ErrorOr>, typename OptionalType = Optional<ConditionallyResultType<IsErrorOr, MappedType>>>
-    ALWAYS_INLINE constexpr Conditional<IsErrorOr, ErrorOr<OptionalType>, OptionalType> map(F&& mapper) const
+    template<typename F,
+        typename MappedType = decltype(declval<F>()(declval<T&>())),
+        auto IsErrorOr = IsSpecializationOf<MappedType, ErrorOr>,
+        typename OptionalType = Optional<ConditionallyResultType<IsErrorOr, MappedType>>,
+        typename Self>
+    ALWAYS_INLINE constexpr Conditional<IsErrorOr, ErrorOr<OptionalType>, OptionalType> map(this Self&& self, F&& mapper)
     {
         if constexpr (IsErrorOr) {
-            if (static_cast<Self const&>(*this).has_value())
-                return OptionalType { TRY(mapper(static_cast<Self const&>(*this).value())) };
+            if (self.has_value())
+                return OptionalType { TRY(mapper(forward<Self>(self).value())) };
             return OptionalType {};
         } else {
-            if (static_cast<Self const&>(*this).has_value())
-                return OptionalType { mapper(static_cast<Self const&>(*this).value()) };
+            if (self.has_value())
+                return OptionalType { mapper(forward<Self>(self).value()) };
 
             return OptionalType {};
         }
@@ -170,7 +157,7 @@ requires(!IsLvalueReference<Self>) class [[nodiscard]] OptionalBase {
 };
 
 template<typename T>
-requires(!IsLvalueReference<T>) class [[nodiscard]] Optional<T> : public OptionalBase<T, Optional<T>> {
+requires(!IsLvalueReference<T>) class [[nodiscard]] Optional<T> : public OptionalBase<T> {
     template<typename U>
     friend class Optional;
 
@@ -509,12 +496,12 @@ requires(IsLvalueReference<T>) class [[nodiscard]] Optional<T> {
 
     [[nodiscard]] ALWAYS_INLINE constexpr bool has_value() const { return m_pointer != nullptr; }
 
-    [[nodiscard]] ALWAYS_INLINE RemoveReference<T>* ptr()
+    [[nodiscard]] ALWAYS_INLINE constexpr RemoveReference<T>* ptr()
     {
         return m_pointer;
     }
 
-    [[nodiscard]] ALWAYS_INLINE RemoveReference<T> const* ptr() const
+    [[nodiscard]] ALWAYS_INLINE constexpr RemoveReference<T> const* ptr() const
     {
         return m_pointer;
     }
@@ -532,7 +519,7 @@ requires(IsLvalueReference<T>) class [[nodiscard]] Optional<T> {
     }
 
     template<typename U>
-    requires(IsBaseOf<RemoveReference<T>, U>) [[nodiscard]] ALWAYS_INLINE constexpr AddConstToReferencedType<T> value_or(U& fallback) const
+    requires(IsBaseOf<RemoveCVReference<T>, U>) [[nodiscard]] ALWAYS_INLINE constexpr AddConstToReferencedType<T> value_or(U& fallback) const
     {
         if (m_pointer)
             return value();
@@ -555,8 +542,8 @@ requires(IsLvalueReference<T>) class [[nodiscard]] Optional<T> {
     ALWAYS_INLINE constexpr AddConstToReferencedType<T> operator*() const { return value(); }
     ALWAYS_INLINE constexpr T operator*() { return value(); }
 
-    ALWAYS_INLINE RawPtr<AddConst<RemoveReference<T>>> operator->() const { return &value(); }
-    ALWAYS_INLINE RawPtr<RemoveReference<T>> operator->() { return &value(); }
+    ALWAYS_INLINE constexpr RawPtr<AddConst<RemoveReference<T>>> operator->() const { return &value(); }
+    ALWAYS_INLINE constexpr RawPtr<RemoveReference<T>> operator->() { return &value(); }
 
     // Conversion operators from Optional<T&> -> Optional<T>, implicit when T is trivially copyable.
     ALWAYS_INLINE constexpr operator Optional<RemoveCVReference<T>>() const
diff --git a/Libraries/LibWeb/CSS/CSSMathClamp.cpp b/Libraries/LibWeb/CSS/CSSMathClamp.cpp
index 6c419e06e2a9..8189f2294bc8 100644
--- a/Libraries/LibWeb/CSS/CSSMathClamp.cpp
+++ b/Libraries/LibWeb/CSS/CSSMathClamp.cpp
@@ -34,7 +34,7 @@ WebIDL::ExceptionOr<GC::Ref<CSSMathClamp>> CSSMathClamp::construct_impl(JS::Real
     // 2. Let type be the result of adding the types of lower, value, and upper. If type is failure, throw a TypeError.
     auto type = lower_rectified->type()
                     .added_to(value_rectified->type())
-                    .map([&](auto& type) { return type.added_to(upper_rectified->type()); });
+                    .map([&](auto&& type) { return type.added_to(upper_rectified->type()); });
     if (!type.has_value()) {
         return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Cannot create a CSSMathClamp with values of incompatible types"sv };
     }
diff --git a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
index 0a1bfa6ce353..4f141121143f 100644
--- a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
+++ b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
@@ -559,7 +559,7 @@ Optional<StyleProperty> CSSStyleProperties::get_direct_property(PropertyNameAndI
     }
 
     if (property_name_and_id.is_custom_property())
-        return custom_property(property_name_and_id.name()).map([](auto& it) { return it; });
+        return custom_property(property_name_and_id.name()).copy();
 
     for (auto const& property : m_properties) {
         if (property.property_id == property_id)
diff --git a/Libraries/LibWeb/CSS/CalculatedOr.cpp b/Libraries/LibWeb/CSS/CalculatedOr.cpp
index 6faa1caec87c..9bf045ff718f 100644
--- a/Libraries/LibWeb/CSS/CalculatedOr.cpp
+++ b/Libraries/LibWeb/CSS/CalculatedOr.cpp
@@ -70,7 +70,7 @@ NonnullRefPtr<StyleValue const> LengthOrCalculated::create_style_value() const
 
 Optional<LengthOrAuto> LengthOrAutoOrCalculated::resolve_calculated(NonnullRefPtr<CalculatedStyleValue const> const& calculated, CalculationResolutionContext const& context) const
 {
-    return calculated->resolve_length(context).map([](auto& length) { return LengthOrAuto { length }; });
+    return calculated->resolve_length(context).map([](auto&& length) { return LengthOrAuto { length }; });
 }
 
 NonnullRefPtr<StyleValue const> LengthOrAutoOrCalculated::create_style_value() const
diff --git a/Libraries/LibWeb/CSS/MediaQuery.cpp b/Libraries/LibWeb/CSS/MediaQuery.cpp
index 588207e4094d..7f6b0b598902 100644
--- a/Libraries/LibWeb/CSS/MediaQuery.cpp
+++ b/Libraries/LibWeb/CSS/MediaQuery.cpp
@@ -125,7 +125,7 @@ MatchResult MediaFeature::evaluate(DOM::Document const* document) const
         if (queried_value.is_ratio())
             return as_match_result(!queried_value.ratio().is_degenerate());
         if (queried_value.is_resolution())
-            return as_match_result(queried_value.resolution().resolved(calculation_context).map([](auto& it) { return it.to_dots_per_pixel(); }).value_or(0) != 0);
+            return as_match_result(queried_value.resolution().resolved(calculation_context).map([](auto&& it) { return it.to_dots_per_pixel(); }).value_or(0) != 0);
         if (queried_value.is_ident()) {
             if (media_feature_keyword_is_falsey(m_id, queried_value.ident()))
                 return MatchResult::False;
@@ -237,8 +237,8 @@ MatchResult MediaFeature::compare(DOM::Document const& document, MediaFeatureVal
     }
 
     if (left.is_resolution()) {
-        auto left_dppx = left.resolution().resolved(calculation_context).map([](auto& it) { return it.to_dots_per_pixel(); }).value_or(0);
-        auto right_dppx = right.resolution().resolved(calculation_context).map([](auto& it) { return it.to_dots_per_pixel(); }).value_or(0);
+        auto left_dppx = left.resolution().resolved(calculation_context).map([](auto&& it) { return it.to_dots_per_pixel(); }).value_or(0);
+        auto right_dppx = right.resolution().resolved(calculation_context).map([](auto&& it) { return it.to_dots_per_pixel(); }).value_or(0);
 
         switch (comparison) {
         case Comparison::Equal:
diff --git a/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Libraries/LibWeb/CSS/Parser/Parser.cpp
index 77a890927eba..4959074b9017 100644
--- a/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1229,7 +1229,7 @@ Optional<Rule> Parser::parse_a_rule(TokenStream<T>& input)
     //    Otherwise, if the next token from input is an <at-keyword-token>,
     //    consume an at-rule from input, and let rule be the return value.
     else if (input.next_token().is(Token::Type::AtKeyword)) {
-        rule = consume_an_at_rule(m_token_stream).map([](auto& it) { return Rule { it }; });
+        rule = consume_an_at_rule(m_token_stream).map([](auto&& it) { return Rule { it }; });
     }
     //    Otherwise, consume a qualified rule from input and let rule be the return value.
     //    If nothing or an invalid rule error was returned, return a syntax error.
diff --git a/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp b/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp
index e1bb7a63f256..1b20719c4508 100644
--- a/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp
+++ b/Libraries/LibWeb/CSS/Parser/PropertyParsing.cpp
@@ -165,7 +165,7 @@ RefPtr<StyleValue const> Parser::parse_coordinating_value_list_shorthand(TokenSt
 RefPtr<StyleValue const> Parser::parse_css_value_for_property(PropertyID property_id, TokenStream<ComponentValue>& tokens)
 {
     return parse_css_value_for_properties({ &property_id, 1 }, tokens)
-        .map([](auto& it) { return it.style_value; })
+        .map([](auto&& it) { return it.style_value; })
         .value_or(nullptr);
 }
 
diff --git a/Libraries/LibWeb/CSS/Parser/ValueParsing.cpp b/Libraries/LibWeb/CSS/Parser/ValueParsing.cpp
index b1cff7ccc2af..04e1adc2743c 100644
--- a/Libraries/LibWeb/CSS/Parser/ValueParsing.cpp
+++ b/Libraries/LibWeb/CSS/Parser/ValueParsing.cpp
@@ -4006,14 +4006,14 @@ Optional<ExplicitGridTrack> Parser::parse_grid_fixed_size(TokenStream<ComponentV
         auto const& function_token = token.function();
         if (function_token.name.equals_ignoring_ascii_case("minmax"sv)) {
             {
-                GridMinMaxParamParser parse_min = [this](auto& tokens) { return parse_grid_fixed_breadth(tokens).map([](auto& it) { return GridSize(Size::make_length_percentage(it)); }); };
+                GridMinMaxParamParser parse_min = [this](auto& tokens) { return parse_grid_fixed_breadth(tokens).map([](auto&& it) { return GridSize(Size::make_length_percentage(it)); }); };
                 GridMinMaxParamParser parse_max = [this](auto& tokens) { return parse_grid_track_breadth(tokens); };
                 if (auto result = parse_grid_minmax(tokens, parse_min, parse_max); result.has_value())
                     return result;
             }
             {
                 GridMinMaxParamParser parse_min = [this](auto& tokens) { return parse_grid_inflexible_breadth(tokens); };
-                GridMinMaxParamParser parse_max = [this](auto& tokens) { return parse_grid_fixed_breadth(tokens).map([](auto& it) { return GridSize(Size::make_length_percentage(it)); }); };
+                GridMinMaxParamParser parse_max = [this](auto& tokens) { return parse_grid_fixed_breadth(tokens).map([](auto&& it) { return GridSize(Size::make_length_percentage(it)); }); };
                 if (auto result = parse_grid_minmax(tokens, parse_min, parse_max); result.has_value())
                     return result;
             }
diff --git a/Libraries/LibWeb/CSS/StyleComputer.cpp b/Libraries/LibWeb/CSS/StyleComputer.cpp
index 74d804579966..cc150808f06e 100644
--- a/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -2558,7 +2558,7 @@ RefPtr<StyleValue const> StyleComputer::recascade_font_size_if_needed(DOM::Abstr
 
         VERIFY(font_size_value->is_length());
 
-        auto inherited_line_height = ancestor.element_to_inherit_style_from().map([](auto& parent_element) { return parent_element.computed_properties()->line_height(); }).value_or(InitialValues::line_height());
+        auto inherited_line_height = ancestor.element_to_inherit_style_from().map([](auto&& parent_element) { return parent_element.computed_properties()->line_height(); }).value_or(InitialValues::line_height());
 
         current_size_in_px = font_size_value->as_length().length().to_px(viewport_rect(), Length::FontMetrics { current_size_in_px, monospace_font->with_size(current_size_in_px * 0.75f)->pixel_metrics(), inherited_line_height }, m_root_element_font_metrics);
     };
diff --git a/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp b/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
index 279ebb399c57..ac52c4bfd803 100644
--- a/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
+++ b/Libraries/LibWeb/CSS/StyleValues/CalculatedStyleValue.cpp
@@ -1271,7 +1271,7 @@ Optional<CalculatedStyleValue::CalculationResult> ClampCalculationNode::run_oper
     if (!max_result.has_value())
         return {};
 
-    auto consistent_type = min_result->type()->consistent_type(center_result->type().value()).map([&](auto& it) { return it.consistent_type(max_result->type().value()); });
+    auto consistent_type = min_result->type()->consistent_type(center_result->type().value()).map([&](auto&& it) { return it.consistent_type(max_result->type().value()); });
     if (!consistent_type.has_value())
         return {};
 
diff --git a/Libraries/LibWeb/DOM/Element.cpp b/Libraries/LibWeb/DOM/Element.cpp
index 7dfd3d28a81e..187f51991c11 100644
--- a/Libraries/LibWeb/DOM/Element.cpp
+++ b/Libraries/LibWeb/DOM/Element.cpp
@@ -852,7 +852,7 @@ CSS::RequiredInvalidationAfterStyleChange Element::recompute_inherited_style()
 
         RefPtr<CSS::StyleValue const> old_animated_value = computed_properties->animated_property_values().get(property_id).value_or({});
         RefPtr<CSS::StyleValue const> new_animated_value = CSS::StyleComputer::get_animated_inherit_value(property_id, { *this })
-                                                               .map([&](auto& value) { return value.ptr(); })
+                                                               .map([](auto&& value) { return value.ptr(); })
                                                                .value_or({});
 
         invalidation |= CSS::compute_property_invalidation(property_id, old_animated_value, new_animated_value);
diff --git a/Libraries/LibWeb/Painting/PaintableBox.cpp b/Libraries/LibWeb/Painting/PaintableBox.cpp
index 3e00a7c32616..ed85e3708a7c 100644
--- a/Libraries/LibWeb/Painting/PaintableBox.cpp
+++ b/Libraries/LibWeb/Painting/PaintableBox.cpp
@@ -1688,7 +1688,7 @@ Optional<Gfx::Filter> PaintableBox::resolve_filter(CSS::Filter const& computed_f
                     .length_resolution_context = CSS::Length::ResolutionContext::for_layout_node(layout_node_with_style_and_box_metrics()),
                 };
                 auto to_px = [&](CSS::LengthOrCalculated const& length) {
-                    return static_cast<float>(length.resolved(context).map([&](auto& it) { return it.to_px(layout_node_with_style_and_box_metrics()).to_double(); }).value_or(0.0));
+                    return static_cast<float>(length.resolved(context).map([&](auto&& it) { return it.to_px(layout_node_with_style_and_box_metrics()).to_double(); }).value_or(0.0));
                 };
                 // The default value for omitted values is missing length values set to 0
                 // and the missing used color is taken from the color property.