diff --git a/components/style/gecko/arc_types.rs b/components/style/gecko/arc_types.rs
index 788f75f2b2f..05fcdb5b12d 100644
--- a/components/style/gecko/arc_types.rs
+++ b/components/style/gecko/arc_types.rs
@@ -10,13 +10,11 @@
 
 use crate::gecko::url::CssUrlData;
 use crate::gecko_bindings::structs::{
-    RawServoAnimationValue, RawServoCounterStyleRule, RawServoCssUrlData,
-    RawServoDeclarationBlock, RawServoFontFaceRule,
-    RawServoFontFeatureValuesRule, RawServoImportRule, RawServoKeyframe,
-    RawServoKeyframesRule, RawServoLayerRule, RawServoMediaList,
-    RawServoMediaRule, RawServoMozDocumentRule, RawServoNamespaceRule,
-    RawServoPageRule, RawServoStyleRule, RawServoStyleSheetContents,
-    RawServoSupportsRule, ServoCssRules
+    RawServoAnimationValue, RawServoCounterStyleRule, RawServoCssUrlData, RawServoDeclarationBlock,
+    RawServoFontFaceRule, RawServoFontFeatureValuesRule, RawServoImportRule, RawServoKeyframe,
+    RawServoKeyframesRule, RawServoLayerRule, RawServoMediaList, RawServoMediaRule,
+    RawServoMozDocumentRule, RawServoNamespaceRule, RawServoPageRule, RawServoScrollTimelineRule,
+    RawServoStyleRule, RawServoStyleSheetContents, RawServoSupportsRule, ServoCssRules,
 };
 use crate::gecko_bindings::sugar::ownership::{HasArcFFI, HasFFI, Strong};
 use crate::media_queries::MediaList;
@@ -25,9 +23,9 @@ use crate::properties::{ComputedValues, PropertyDeclarationBlock};
 use crate::shared_lock::Locked;
 use crate::stylesheets::keyframes_rule::Keyframe;
 use crate::stylesheets::{
-    CounterStyleRule, CssRules, FontFaceRule, FontFeatureValuesRule,
-    DocumentRule, ImportRule, KeyframesRule, LayerRule, MediaRule,
-    NamespaceRule, PageRule, StyleRule, StylesheetContents, SupportsRule
+    CounterStyleRule, CssRules, DocumentRule, FontFaceRule, FontFeatureValuesRule, ImportRule,
+    KeyframesRule, LayerRule, MediaRule, NamespaceRule, PageRule, ScrollTimelineRule, StyleRule,
+    StylesheetContents, SupportsRule,
 };
 use servo_arc::{Arc, ArcBorrow};
 use std::{mem, ptr};
@@ -90,6 +88,9 @@ impl_arc_ffi!(Locked<NamespaceRule> => RawServoNamespaceRule
 impl_arc_ffi!(Locked<PageRule> => RawServoPageRule
               [Servo_PageRule_AddRef, Servo_PageRule_Release]);
 
+impl_arc_ffi!(Locked<ScrollTimelineRule> => RawServoScrollTimelineRule
+              [Servo_ScrollTimelineRule_AddRef, Servo_ScrollTimelineRule_Release]);
+
 impl_arc_ffi!(Locked<SupportsRule> => RawServoSupportsRule
               [Servo_SupportsRule_AddRef, Servo_SupportsRule_Release]);
 
diff --git a/components/style/stylesheets/scroll_timeline_rule.rs b/components/style/stylesheets/scroll_timeline_rule.rs
index f11e469f958..bbc5d9caf8f 100644
--- a/components/style/stylesheets/scroll_timeline_rule.rs
+++ b/components/style/stylesheets/scroll_timeline_rule.rs
@@ -169,6 +169,12 @@ pub enum Source {
     None,
 }
 
+impl Default for Source {
+    fn default() -> Self {
+        Source::Auto
+    }
+}
+
 /// The scroll-timeline orientation.
 /// https://drafts.csswg.org/scroll-animations/#descdef-scroll-timeline-orientation
 ///
@@ -189,11 +195,17 @@ pub enum Orientation {
     Vertical,
 }
 
+impl Default for Orientation {
+    fn default() -> Self {
+        Orientation::Auto
+    }
+}
+
 /// Scroll-timeline offsets. We treat None as an empty vector.
 /// value: none | <scroll-timeline-offset>#
 ///
 /// https://drafts.csswg.org/scroll-animations/#descdef-scroll-timeline-scroll-offsets
-#[derive(Clone, Debug, ToCss, ToShmem)]
+#[derive(Clone, Default, Debug, ToCss, ToShmem)]
 #[css(comma)]
 pub struct ScrollOffsets(#[css(if_empty = "none", iterable)] Box<[ScrollTimelineOffset]>);