diff --git a/Libraries/LibWeb/CSS/PseudoElements.json b/Libraries/LibWeb/CSS/PseudoElements.json
index 29a87a55389..f2847166fb6 100644
--- a/Libraries/LibWeb/CSS/PseudoElements.json
+++ b/Libraries/LibWeb/CSS/PseudoElements.json
@@ -50,19 +50,61 @@
     "spec": "https://drafts.csswg.org/css-forms-1/#selectordef-fill"
   },
   "first-letter": {
-    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-first-letter"
+    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-first-letter",
+    "property-whitelist": [
+      "#font-properties",
+      "color",
+      "opacity",
+      "#background-properties",
+      "#inline-typesetting-properties",
+      "#text-decoration-properties",
+      "#inline-layout-properties",
+      "#margin-properties",
+      "#padding-properties",
+      "#border-properties",
+      "box-shadow"
+    ]
   },
   "first-line": {
-    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-first-line"
+    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-first-line",
+    "property-whitelist": [
+      "#font-properties",
+      "color",
+      "opacity",
+      "#background-properties",
+      "#inline-typesetting-properties",
+      "#text-decoration-properties",
+      "FIXME: ruby-position",
+      "#inline-layout-properties"
+    ]
   },
   "marker": {
     "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-marker"
   },
   "placeholder": {
-    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-placeholder"
+    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-placeholder",
+    "property-whitelist": [
+      "#font-properties",
+      "color",
+      "opacity",
+      "#background-properties",
+      "#inline-typesetting-properties",
+      "#text-decoration-properties",
+      "FIXME: ruby-position"
+    ]
   },
   "selection": {
-    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-selection"
+    "spec": "https://drafts.csswg.org/css-pseudo-4/#selectordef-selection",
+    "property-whitelist": [
+      "color",
+      "background-color",
+      "#text-decoration-properties",
+      "text-shadow",
+      "FIXME: stroke-color",
+      "FIXME: fill-color",
+      "stroke-width",
+      "#custom-properties"
+    ]
   },
   "thumb": {
     "spec": "https://drafts.csswg.org/css-forms-1/#selectordef-thumb"
diff --git a/Meta/Lagom/Tools/CodeGenerators/LibWeb/GenerateCSSPseudoElement.cpp b/Meta/Lagom/Tools/CodeGenerators/LibWeb/GenerateCSSPseudoElement.cpp
index 49038b7df1b..2a1659ea498 100644
--- a/Meta/Lagom/Tools/CodeGenerators/LibWeb/GenerateCSSPseudoElement.cpp
+++ b/Meta/Lagom/Tools/CodeGenerators/LibWeb/GenerateCSSPseudoElement.cpp
@@ -58,6 +58,7 @@ ErrorOr<void> generate_header_file(JsonObject& pseudo_elements_data, Core::File&
 
 #include <AK/Optional.h>
 #include <AK/StringView.h>
+#include <LibWeb/CSS/PropertyID.h>
 
 namespace Web::CSS {
 
@@ -85,6 +86,7 @@ Optional<PseudoElement> aliased_pseudo_element_from_string(StringView);
 StringView pseudo_element_name(PseudoElement);
 
 bool is_has_allowed_pseudo_element(PseudoElement);
+bool pseudo_element_supports_property(PseudoElement, PropertyID);
 
 enum class GeneratedPseudoElement : @generated_pseudo_element_underlying_type@ {
 )~~~");
@@ -222,6 +224,245 @@ bool is_has_allowed_pseudo_element(PseudoElement pseudo_element)
     }
 }
 
+bool pseudo_element_supports_property(PseudoElement pseudo_element, PropertyID property_id)
+{
+    switch (pseudo_element) {
+)~~~");
+
+    pseudo_elements_data.for_each_member([&](auto& name, JsonValue const& value) {
+        auto& pseudo_element = value.as_object();
+        if (pseudo_element.has("alias-for"sv))
+            return;
+        auto property_whitelist = pseudo_element.get_array("property-whitelist"sv);
+        // No whitelist = accept everything, by falling back to the default case.
+        if (!property_whitelist.has_value())
+            return;
+
+        auto member_generator = generator.fork();
+        member_generator.set("name:titlecase", title_casify(name));
+        member_generator.append(R"~~~(
+    case PseudoElement::@name:titlecase@:
+        switch (property_id) {
+)~~~");
+
+        property_whitelist->for_each([&](JsonValue const& entry) {
+            auto& property = entry.as_string();
+            if (property.starts_with_bytes("FIXME:"sv))
+                return;
+
+            auto append_property = [&](StringView const& property_name) {
+                auto property_generator = member_generator.fork();
+                property_generator.set("property:titlecase", title_casify(property_name));
+                property_generator.appendln("        case PropertyID::@property:titlecase@:");
+            };
+
+            if (!property.starts_with('#')) {
+                append_property(property);
+                return;
+            }
+            // Categories
+            // TODO: Maybe define these in data somewhere too?
+            if (property == "#background-properties"sv) {
+                // https://drafts.csswg.org/css-backgrounds/#property-index
+                append_property("background"sv);
+                append_property("background-attachment"sv);
+                append_property("background-clip"sv);
+                append_property("background-color"sv);
+                append_property("background-image"sv);
+                append_property("background-origin"sv);
+                append_property("background-position"sv);
+                append_property("background-position-x"sv);
+                append_property("background-position-y"sv);
+                append_property("background-repeat"sv);
+                append_property("background-size"sv);
+                return;
+            }
+            if (property == "#border-properties"sv) {
+                // https://drafts.csswg.org/css-backgrounds/#property-index
+                append_property("border"sv);
+                append_property("border-block-end"sv);
+                append_property("border-block-end-color"sv);
+                append_property("border-block-end-style"sv);
+                append_property("border-block-end-width"sv);
+                append_property("border-block-start"sv);
+                append_property("border-block-start-color"sv);
+                append_property("border-block-start-style"sv);
+                append_property("border-block-start-width"sv);
+                append_property("border-bottom"sv);
+                append_property("border-bottom-color"sv);
+                append_property("border-bottom-left-radius"sv);
+                append_property("border-bottom-right-radius"sv);
+                append_property("border-bottom-style"sv);
+                append_property("border-bottom-width"sv);
+                append_property("border-color"sv);
+                append_property("border-inline-end"sv);
+                append_property("border-inline-end-color"sv);
+                append_property("border-inline-end-style"sv);
+                append_property("border-inline-end-width"sv);
+                append_property("border-inline-start"sv);
+                append_property("border-inline-start-color"sv);
+                append_property("border-inline-start-style"sv);
+                append_property("border-inline-start-width"sv);
+                append_property("border-left"sv);
+                append_property("border-left-color"sv);
+                append_property("border-left-style"sv);
+                append_property("border-left-width"sv);
+                append_property("border-radius"sv);
+                append_property("border-right"sv);
+                append_property("border-right-color"sv);
+                append_property("border-right-style"sv);
+                append_property("border-right-width"sv);
+                append_property("border-style"sv);
+                append_property("border-top"sv);
+                append_property("border-top-color"sv);
+                append_property("border-top-left-radius"sv);
+                append_property("border-top-right-radius"sv);
+                append_property("border-top-style"sv);
+                append_property("border-top-width"sv);
+                append_property("border-width"sv);
+                return;
+            }
+            if (property == "#custom-properties"sv) {
+                append_property("custom"sv);
+                return;
+            }
+            if (property == "#font-properties"sv) {
+                // https://drafts.csswg.org/css-fonts/#property-index
+                append_property("font"sv);
+                append_property("font-family"sv);
+                append_property("font-feature-settings"sv);
+                // FIXME: font-kerning
+                append_property("font-language-override"sv);
+                // FIXME: font-optical-sizing
+                // FIXME: font-palette
+                append_property("font-size"sv);
+                // FIXME: font-size-adjust
+                append_property("font-style"sv);
+                // FIXME: font-synthesis and longhands
+                append_property("font-variant"sv);
+                append_property("font-variant-alternates"sv);
+                append_property("font-variant-caps"sv);
+                append_property("font-variant-east-asian"sv);
+                append_property("font-variant-emoji"sv);
+                append_property("font-variant-ligatures"sv);
+                append_property("font-variant-numeric"sv);
+                append_property("font-variant-position"sv);
+                append_property("font-variation-settings"sv);
+                append_property("font-weight"sv);
+                append_property("font-width"sv);
+                return;
+            }
+            if (property == "#inline-layout-properties"sv) {
+                // https://drafts.csswg.org/css-inline/#property-index
+                // FIXME: alignment-baseline
+                // FIXME: baseline-shift
+                // FIXME: baseline-source
+                // FIXME: dominant-baseline
+                // FIXME: initial-letter
+                // FIXME: initial-letter-align
+                // FIXME: initial-letter-wrap
+                // FIXME: inline-sizing
+                // FIXME: line-edge-fit
+                append_property("line-height"sv);
+                // FIXME: text-box
+                // FIXME: text-box-edge
+                // FIXME: text-box-trim
+                append_property("vertical-align"sv);
+                return;
+            }
+            if (property == "#inline-typesetting-properties"sv) {
+                // https://drafts.csswg.org/css-text-4/#property-index
+                // FIXME: hanging-punctuation
+                // FIXME: hyphenate-character
+                // FIXME: hyphenate-limit-chars
+                // FIXME: hyphenate-limit-last
+                // FIXME: hyphenate-limit-lines
+                // FIXME: hyphenate-limit-zone
+                // FIXME: hyphens
+                append_property("letter-spacing"sv);
+                // FIXME: line-break
+                // FIXME: line-padding
+                // FIXME: overflow-wrap
+                append_property("tab-size"sv);
+                append_property("text-align"sv);
+                // FIXME: text-align-all
+                // FIXME: text-align-last
+                // FIXME: text-autospace
+                // FIXME: text-group-align
+                append_property("text-indent"sv);
+                append_property("text-justify"sv);
+                // FIXME: text-spacing
+                // FIXME: text-spacing-trim
+                append_property("text-transform"sv);
+                // FIXME: text-wrap
+                // FIXME: text-wrap-mode
+                // FIXME: text-wrap-style
+                append_property("white-space"sv);
+                // FIXME: white-space-collapse
+                // FIXME: white-space-trim
+                append_property("word-break"sv);
+                // FIXME: word-space-transform
+                append_property("word-spacing"sv);
+                append_property("word-wrap"sv);
+                // FIXME: wrap-after
+                // FIXME: wrap-before
+                // FIXME: wrap-inside
+                return;
+            }
+            if (property == "#margin-properties"sv) {
+                append_property("margin"sv);
+                append_property("margin-block"sv);
+                append_property("margin-block-end"sv);
+                append_property("margin-block-start"sv);
+                append_property("margin-bottom"sv);
+                append_property("margin-inline"sv);
+                append_property("margin-inline-end"sv);
+                append_property("margin-inline-start"sv);
+                append_property("margin-left"sv);
+                append_property("margin-right"sv);
+                append_property("margin-top"sv);
+                return;
+            }
+            if (property == "#padding-properties"sv) {
+                append_property("padding"sv);
+                append_property("padding-block"sv);
+                append_property("padding-block-end"sv);
+                append_property("padding-block-start"sv);
+                append_property("padding-bottom"sv);
+                append_property("padding-inline"sv);
+                append_property("padding-inline-end"sv);
+                append_property("padding-inline-start"sv);
+                append_property("padding-left"sv);
+                append_property("padding-right"sv);
+                append_property("padding-top"sv);
+                return;
+            }
+            if (property == "#text-decoration-properties"sv) {
+                append_property("text-decoration"sv);
+                append_property("text-decoration-color"sv);
+                append_property("text-decoration-line"sv);
+                append_property("text-decoration-style"sv);
+                append_property("text-decoration-thickness"sv);
+                return;
+            }
+            outln("Error: Unrecognized property group name '{}' in {}", property, name);
+            exit(1);
+        });
+
+        member_generator.append(R"~~~(
+            return true;
+        default:
+            return false;
+        }
+)~~~");
+    });
+
+    generator.append(R"~~~(
+    default:
+        return true;
+    }
+}
+
 Optional<GeneratedPseudoElement> to_generated_pseudo_element(PseudoElement pseudo_element)
 {
     switch (pseudo_element) {