diff --git a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
index 71f193a09d8..19309dfd6cc 100644
--- a/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
+++ b/Libraries/LibWeb/CSS/CSSStyleProperties.cpp
@@ -270,9 +270,13 @@ WebIDL::ExceptionOr<void> CSSStyleProperties::set_property(StringView property_n
     }
 
     // 10. If updated is true, update style attribute for the CSS declaration block.
-    if (updated)
+    if (updated) {
         update_style_attribute();
 
+        // Non-standard: Invalidate style for the owners of our containing sheet, if any.
+        invalidate_owners(DOM::StyleInvalidationReason::CSSStylePropertiesSetProperty);
+    }
+
     return {};
 }
 
@@ -1049,9 +1053,13 @@ WebIDL::ExceptionOr<String> CSSStyleProperties::remove_property(StringView prope
     }
 
     // 7. If removed is true, Update style attribute for the CSS declaration block.
-    if (removed)
+    if (removed) {
         update_style_attribute();
 
+        // Non-standard: Invalidate style for the owners of our containing sheet, if any.
+        invalidate_owners(DOM::StyleInvalidationReason::CSSStylePropertiesRemoveProperty);
+    }
+
     // 8. Return value.
     return value;
 }
@@ -1164,15 +1172,20 @@ WebIDL::ExceptionOr<void> CSSStyleProperties::set_css_text(StringView css_text)
     update_style_attribute();
 
     // Non-standard: Invalidate style for the owners of our containing sheet, if any.
-    if (auto rule = parent_rule()) {
-        if (auto sheet = rule->parent_style_sheet()) {
-            sheet->invalidate_owners(DOM::StyleInvalidationReason::CSSStylePropertiesTextChange);
-        }
-    }
+    invalidate_owners(DOM::StyleInvalidationReason::CSSStylePropertiesTextChange);
 
     return {};
 }
 
+void CSSStyleProperties::invalidate_owners(DOM::StyleInvalidationReason reason)
+{
+    if (auto rule = parent_rule()) {
+        if (auto sheet = rule->parent_style_sheet()) {
+            sheet->invalidate_owners(reason);
+        }
+    }
+}
+
 // https://drafts.csswg.org/cssom/#set-a-css-declaration
 bool CSSStyleProperties::set_a_css_declaration(PropertyID property_id, NonnullRefPtr<CSSStyleValue const> value, Important important)
 {
diff --git a/Libraries/LibWeb/CSS/CSSStyleProperties.h b/Libraries/LibWeb/CSS/CSSStyleProperties.h
index a6405248f4a..69326048a28 100644
--- a/Libraries/LibWeb/CSS/CSSStyleProperties.h
+++ b/Libraries/LibWeb/CSS/CSSStyleProperties.h
@@ -71,6 +71,8 @@ private:
     void empty_the_declarations();
     void set_the_declarations(Vector<StyleProperty> properties, HashMap<FlyString, StyleProperty> custom_properties);
 
+    void invalidate_owners(DOM::StyleInvalidationReason);
+
     Vector<StyleProperty> m_properties;
     HashMap<FlyString, StyleProperty> m_custom_properties;
 };
diff --git a/Libraries/LibWeb/CSS/CSSStyleSheet.cpp b/Libraries/LibWeb/CSS/CSSStyleSheet.cpp
index eb33f279cfc..6b3b639bef1 100644
--- a/Libraries/LibWeb/CSS/CSSStyleSheet.cpp
+++ b/Libraries/LibWeb/CSS/CSSStyleSheet.cpp
@@ -248,6 +248,11 @@ WebIDL::ExceptionOr<void> CSSStyleSheet::replace_sync(StringView text)
             rules_without_import.append(rule);
     }
 
+    // NOTE: The spec doesn't say where to set the parent style sheet, so we'll do it here.
+    for (auto& rule : rules_without_import) {
+        rule->set_parent_style_sheet(this);
+    }
+
     // 4. Set sheet’s CSS rules to rules.
     m_rules->set_rules({}, rules_without_import);
 
diff --git a/Libraries/LibWeb/DOM/Node.h b/Libraries/LibWeb/DOM/Node.h
index 4718ebf2a42..9426c8ad2a8 100644
--- a/Libraries/LibWeb/DOM/Node.h
+++ b/Libraries/LibWeb/DOM/Node.h
@@ -52,6 +52,8 @@ enum class ShouldComputeRole {
     X(AdoptedStyleSheetsList)                       \
     X(CSSFontLoaded)                                \
     X(CSSImportRule)                                \
+    X(CSSStylePropertiesRemoveProperty)             \
+    X(CSSStylePropertiesSetProperty)                \
     X(CSSStylePropertiesTextChange)                 \
     X(CustomElementStateChange)                     \
     X(DidLoseFocus)                                 \
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/cssom/CSSStyleSheet-constructable-invalidation.txt b/Tests/LibWeb/Text/expected/wpt-import/css/cssom/CSSStyleSheet-constructable-invalidation.txt
new file mode 100644
index 00000000000..b8fecef6a39
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/cssom/CSSStyleSheet-constructable-invalidation.txt
@@ -0,0 +1,9 @@
+Harness status: OK
+
+Found 3 tests
+
+2 Pass
+1 Fail
+Fail	mutating constructed CSSStyleSheet applied to root invalidates styles
+Pass	mutating constructed CSSStyleSheet applied to shadowdom invalidates styles
+Pass	mutating dependent constructed CSSStyleSheet applied to shadowdom invalidates styles
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/cssom/CSSStyleSheet-constructable-invalidation.html b/Tests/LibWeb/Text/input/wpt-import/css/cssom/CSSStyleSheet-constructable-invalidation.html
new file mode 100644
index 00000000000..022ceecc1cf
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/css/cssom/CSSStyleSheet-constructable-invalidation.html
@@ -0,0 +1,49 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>CSSStyleSheet rule mutation invalidation</title>
+<link rel="author" href="mailto:wpt@keithcirkel.co.uk" title="Keith Cirkel">
+<link rel="help" href="https://drafts.csswg.org/cssom/#extensions-to-the-document-or-shadow-root-interface">
+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<span id="span1">Should be green.</span>
+<span id="span2">Should be green.</span>
+<script>
+promise_test(async function(t) {
+  const sheet = new CSSStyleSheet();
+  sheet.replaceSync('span {color:var(--color, red);}');
+  document.adoptedStyleSheets = [sheet];
+  t.add_cleanup(() => {
+    document.adoptedStyleSheets = [];
+  })
+  assert_equals(getComputedStyle(span1).color, "rgb(255, 0, 0)", "Sheet should apply");
+  sheet.rules[0].style.setProperty('--color', 'green');
+  assert_equals(getComputedStyle(span1).color, "rgb(0, 128, 0)", "Sheet should invalidate style");
+  document.adoptedStyleSheets = [];
+  assert_equals(getComputedStyle(span1).color, "rgb(0, 0, 0)", "Removing sheet should apply");
+}, "mutating constructed CSSStyleSheet applied to root invalidates styles");
+
+promise_test(async function() {
+  span1.attachShadow({mode:'open'})
+  span1.shadowRoot.append(document.createElement('slot'))
+  const sheet = new CSSStyleSheet();
+  sheet.replaceSync(':host {color:var(--color, red);}');
+  span1.shadowRoot.adoptedStyleSheets = [sheet];
+  assert_equals(getComputedStyle(span1).color, "rgb(255, 0, 0)", "Sheet should apply");
+  sheet.rules[0].style.setProperty('--color', 'green');
+  assert_equals(getComputedStyle(span1).color, "rgb(0, 128, 0)", "Sheet should invalidate style");
+}, "mutating constructed CSSStyleSheet applied to shadowdom invalidates styles");
+
+promise_test(async function() {
+  span2.attachShadow({mode:'open'})
+  span2.shadowRoot.append(document.createElement('slot'))
+  const sheet1 = new CSSStyleSheet();
+  const sheet2 = new CSSStyleSheet();
+  sheet1.replaceSync(':host {color:var(--color, hotpink);}');
+  sheet2.replaceSync(':host {--color: blue}');
+  const style2 = sheet2.rules[0].style;
+  span2.shadowRoot.adoptedStyleSheets = [sheet1, sheet2];
+  assert_equals(getComputedStyle(span2).color, "rgb(0, 0, 255)", "Sheet should apply");
+  style2.setProperty('--color', 'green');
+  assert_equals(getComputedStyle(span2).color, "rgb(0, 128, 0)", "Sheet should invalidate style");
+}, "mutating dependent constructed CSSStyleSheet applied to shadowdom invalidates styles");
+</script>