diff --git a/Libraries/LibWeb/CSS/CSSMediaRule.h b/Libraries/LibWeb/CSS/CSSMediaRule.h
index b64a2fc9b9a..e0dd578223e 100644
--- a/Libraries/LibWeb/CSS/CSSMediaRule.h
+++ b/Libraries/LibWeb/CSS/CSSMediaRule.h
@@ -24,6 +24,8 @@ public:
     virtual ~CSSMediaRule() = default;
 
     virtual String condition_text() const override;
+    bool matches() const { return condition_matches(); }
+
     virtual bool condition_matches() const override { return m_media->matches(); }
 
     MediaList* media() const { return m_media; }
diff --git a/Libraries/LibWeb/CSS/CSSMediaRule.idl b/Libraries/LibWeb/CSS/CSSMediaRule.idl
index 7aea427789b..b4edaea781d 100644
--- a/Libraries/LibWeb/CSS/CSSMediaRule.idl
+++ b/Libraries/LibWeb/CSS/CSSMediaRule.idl
@@ -5,4 +5,5 @@
 [Exposed=Window]
 interface CSSMediaRule : CSSConditionRule {
     [SameObject, PutForwards=mediaText] readonly attribute MediaList media;
+    readonly attribute boolean matches;
 };
diff --git a/Libraries/LibWeb/CSS/CSSSupportsRule.h b/Libraries/LibWeb/CSS/CSSSupportsRule.h
index 215632550c5..8de559592b7 100644
--- a/Libraries/LibWeb/CSS/CSSSupportsRule.h
+++ b/Libraries/LibWeb/CSS/CSSSupportsRule.h
@@ -25,6 +25,8 @@ public:
     virtual ~CSSSupportsRule() = default;
 
     String condition_text() const override;
+    bool matches() const { return condition_matches(); }
+
     virtual bool condition_matches() const override { return m_supports->matches(); }
 
     Supports const& supports() const { return m_supports; }
diff --git a/Libraries/LibWeb/CSS/CSSSupportsRule.idl b/Libraries/LibWeb/CSS/CSSSupportsRule.idl
index 4c3c19930c8..03eed837c11 100644
--- a/Libraries/LibWeb/CSS/CSSSupportsRule.idl
+++ b/Libraries/LibWeb/CSS/CSSSupportsRule.idl
@@ -3,4 +3,5 @@
 // https://drafts.csswg.org/css-conditional-3/#the-csssupportsrule-interface
 [Exposed=Window]
 interface CSSSupportsRule : CSSConditionRule {
+    readonly attribute boolean matches;
 };
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/idlharness.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/idlharness.txt
new file mode 100644
index 00000000000..b2b837e0fe7
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/idlharness.txt
@@ -0,0 +1,50 @@
+Harness status: OK
+
+Found 45 tests
+
+45 Pass
+Pass	idl_test setup
+Pass	idl_test validation
+Pass	Partial interface CSSRule: original interface defined
+Pass	Partial interface CSSRule: member names are unique
+Pass	Partial namespace CSS: original namespace defined
+Pass	Partial namespace CSS: member names are unique
+Pass	CSSConditionRule interface: existence and properties of interface object
+Pass	CSSConditionRule interface object length
+Pass	CSSConditionRule interface object name
+Pass	CSSConditionRule interface: existence and properties of interface prototype object
+Pass	CSSConditionRule interface: existence and properties of interface prototype object's "constructor" property
+Pass	CSSConditionRule interface: existence and properties of interface prototype object's @@unscopables property
+Pass	CSSConditionRule interface: attribute conditionText
+Pass	CSSMediaRule interface: existence and properties of interface object
+Pass	CSSMediaRule interface object length
+Pass	CSSMediaRule interface object name
+Pass	CSSMediaRule interface: existence and properties of interface prototype object
+Pass	CSSMediaRule interface: existence and properties of interface prototype object's "constructor" property
+Pass	CSSMediaRule interface: existence and properties of interface prototype object's @@unscopables property
+Pass	CSSMediaRule interface: attribute media
+Pass	CSSMediaRule interface: attribute matches
+Pass	CSSMediaRule must be primary interface of cssMediaRule
+Pass	Stringification of cssMediaRule
+Pass	CSSMediaRule interface: cssMediaRule must inherit property "media" with the proper type
+Pass	CSSMediaRule interface: cssMediaRule must inherit property "matches" with the proper type
+Pass	CSSConditionRule interface: cssMediaRule must inherit property "conditionText" with the proper type
+Pass	CSSRule interface: cssMediaRule must inherit property "SUPPORTS_RULE" with the proper type
+Pass	CSSSupportsRule interface: existence and properties of interface object
+Pass	CSSSupportsRule interface object length
+Pass	CSSSupportsRule interface object name
+Pass	CSSSupportsRule interface: existence and properties of interface prototype object
+Pass	CSSSupportsRule interface: existence and properties of interface prototype object's "constructor" property
+Pass	CSSSupportsRule interface: existence and properties of interface prototype object's @@unscopables property
+Pass	CSSSupportsRule interface: attribute matches
+Pass	CSSSupportsRule must be primary interface of cssSupportsRule
+Pass	Stringification of cssSupportsRule
+Pass	CSSSupportsRule interface: cssSupportsRule must inherit property "matches" with the proper type
+Pass	CSSConditionRule interface: cssSupportsRule must inherit property "conditionText" with the proper type
+Pass	CSSRule interface: cssSupportsRule must inherit property "SUPPORTS_RULE" with the proper type
+Pass	CSSRule interface: constant SUPPORTS_RULE on interface object
+Pass	CSSRule interface: constant SUPPORTS_RULE on interface prototype object
+Pass	CSSRule interface: cssRule must inherit property "SUPPORTS_RULE" with the proper type
+Pass	CSS namespace: operation escape(CSSOMString)
+Pass	CSS namespace: operation supports(CSSOMString, CSSOMString)
+Pass	CSS namespace: operation supports(CSSOMString)
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/css-conditional/idlharness.html b/Tests/LibWeb/Text/input/wpt-import/css/css-conditional/idlharness.html
new file mode 100644
index 00000000000..6c253dc3ea6
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/css/css-conditional/idlharness.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+<html>
+
+<head>
+  <meta charset="utf-8">
+  <title>CSS Conditional Rules IDL tests</title>
+  <link rel="help" href="https://drafts.csswg.org/css-conditional/">
+  <script src="../../resources/testharness.js"></script>
+  <script src="../../resources/testharnessreport.js"></script>
+  <script src="../../resources/WebIDLParser.js"></script>
+  <script src="../../resources/idlharness.js"></script>
+  <!-- used to provide objects -->
+  <style>
+    div { display: block; }
+  </style>
+  <style>
+    @media print { }
+  </style>
+  <style>
+    @supports (display: block) { }
+  </style>
+</head>
+
+<body>
+  <div id="log"></div>
+
+  <script>
+    'use strict';
+    idl_test(
+      ['css-conditional'],
+      ['cssom', 'dom'],
+      idl_array => {
+        idl_array.add_objects({
+          CSSRule: ['cssRule'],
+          CSSMediaRule: ['cssMediaRule'],
+          CSSSupportsRule: ['cssSupportsRule'],
+        });
+        self.cssRule = document.styleSheets[0].cssRules[0];
+        self.cssMediaRule = document.styleSheets[1].cssRules[0];
+        self.cssSupportsRule = document.styleSheets[2].cssRules[0];
+      }
+    );
+  </script>
+
+</body>
+
+</html>
diff --git a/Tests/LibWeb/Text/input/wpt-import/interfaces/css-conditional.idl b/Tests/LibWeb/Text/input/wpt-import/interfaces/css-conditional.idl
new file mode 100644
index 00000000000..eace34c0f49
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/interfaces/css-conditional.idl
@@ -0,0 +1,29 @@
+// GENERATED CONTENT - DO NOT EDIT
+// Content was automatically extracted by Reffy into webref
+// (https://github.com/w3c/webref)
+// Source: CSS Conditional Rules Module Level 3 (https://drafts.csswg.org/css-conditional-3/)
+
+partial interface CSSRule {
+    const unsigned short SUPPORTS_RULE = 12;
+};
+
+[Exposed=Window]
+interface CSSConditionRule : CSSGroupingRule {
+    readonly attribute CSSOMString conditionText;
+};
+
+[Exposed=Window]
+interface CSSMediaRule : CSSConditionRule {
+    [SameObject, PutForwards=mediaText] readonly attribute MediaList media;
+    readonly attribute boolean matches;
+};
+
+[Exposed=Window]
+interface CSSSupportsRule : CSSConditionRule {
+  readonly attribute boolean matches;
+};
+
+partial namespace CSS {
+  boolean supports(CSSOMString property, CSSOMString value);
+  boolean supports(CSSOMString conditionText);
+};