diff --git a/lib/widgets/pluri_layout.dart b/lib/widgets/pluri_layout.dart
index 0bffd11..a5fba7b 100644
--- a/lib/widgets/pluri_layout.dart
+++ b/lib/widgets/pluri_layout.dart
@@ -5,7 +5,16 @@ import 'mini_reproductor.dart';
 import 'pluri_bottom_navigation.dart';
 
 abstract final class PluriLayout {
+  // S5 (Tier 1 visual fidelity): the prototype (`t4`) runs a 3-tier
+  // horizontal padding scale — 20px for section titles/eyebrows (lines
+  // 153, 254, 299, 511), 16px for cards (lines 327, 512, 610), 12px for
+  // background-less list rows (lines 174, 226, 301). [horizontal] IS the
+  // card tier — its value and every existing call site stay unchanged;
+  // [titleHorizontal] and [rowHorizontal] are new.
+  static const double titleHorizontal = 20;
   static const double horizontal = 16;
+  static const double rowHorizontal = 12;
+
   static const double sectionGap = 12;
   static const double panelGap = 12;
   static const double compactGap = 8;
@@ -36,6 +45,12 @@ abstract final class PluriLayout {
     horizontal: horizontal,
   );
 
+  /// S5: the title/eyebrow tier's own content padding — e.g. a section
+  /// heading living directly on the page background, outside any card.
+  static const EdgeInsets titleContentPadding = EdgeInsets.symmetric(
+    horizontal: titleHorizontal,
+  );
+
   static const EdgeInsets sheetPadding = EdgeInsets.all(18);
 }
 
diff --git a/test/widgets/pluri_layout_test.dart b/test/widgets/pluri_layout_test.dart
new file mode 100644
index 0000000..df2b25c
--- /dev/null
+++ b/test/widgets/pluri_layout_test.dart
@@ -0,0 +1,29 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pluriwave/widgets/pluri_layout.dart';
+
+/// S5 (Tier 1 visual fidelity): the prototype runs a 3-tier horizontal
+/// padding scale (`t4`) — 20px for section titles/eyebrows (lines 153, 254,
+/// 299, 511), 16px for cards (lines 327, 512, 610), 12px for
+/// background-less list rows (lines 174, 226, 301). The build had
+/// collapsed all three into a single `PluriLayout.horizontal = 16`.
+void main() {
+  test('titleHorizontal is 20 — the prototype\'s title/eyebrow tier', () {
+    expect(PluriLayout.titleHorizontal, 20);
+  });
+
+  test('horizontal (the card tier) stays 16 — unchanged', () {
+    expect(PluriLayout.horizontal, 16);
+  });
+
+  test('rowHorizontal is 12 — the prototype\'s background-less row tier', () {
+    expect(PluriLayout.rowHorizontal, 12);
+  });
+
+  test('titleContentPadding is symmetric horizontal titleHorizontal', () {
+    expect(
+      PluriLayout.titleContentPadding,
+      const EdgeInsets.symmetric(horizontal: PluriLayout.titleHorizontal),
+    );
+  });
+}