From 11fae79346a29e46da4a0fe7e51b88fc3f82cf4e Mon Sep 17 00:00:00 2001
From: Cyrus Gray <144336577+graycyrus@users.noreply.github.com>
Date: Fri, 5 Jun 2026 17:45:10 +0530
Subject: [PATCH] feat(appearance): add global font size setting (#3120)
 (#3396)

---
 .../settings/panels/AppearancePanel.test.tsx  |  48 ++++++++
 .../settings/panels/AppearancePanel.tsx       | 104 ++++++++++++++++++
 app/src/lib/i18n/ar.ts                        |  12 ++
 app/src/lib/i18n/bn.ts                        |  12 ++
 app/src/lib/i18n/de.ts                        |  12 ++
 app/src/lib/i18n/en.ts                        |  12 ++
 app/src/lib/i18n/es.ts                        |  12 ++
 app/src/lib/i18n/fr.ts                        |  12 ++
 app/src/lib/i18n/hi.ts                        |  12 ++
 app/src/lib/i18n/id.ts                        |  12 ++
 app/src/lib/i18n/it.ts                        |  12 ++
 app/src/lib/i18n/ko.ts                        |  12 ++
 app/src/lib/i18n/pl.ts                        |  12 ++
 app/src/lib/i18n/pt.ts                        |  12 ++
 app/src/lib/i18n/ru.ts                        |  12 ++
 app/src/lib/i18n/zh-CN.ts                     |  12 ++
 app/src/providers/ThemeProvider.test.tsx      |  32 ++++++
 app/src/providers/ThemeProvider.tsx           |  26 ++++-
 app/src/store/index.ts                        |   2 +-
 app/src/store/themeSlice.test.ts              |  41 +++++++
 app/src/store/themeSlice.ts                   |  27 ++++-
 app/src/test/test-utils.tsx                   |   5 +-
 22 files changed, 443 insertions(+), 10 deletions(-)
 create mode 100644 app/src/components/settings/panels/AppearancePanel.test.tsx
 create mode 100644 app/src/providers/ThemeProvider.test.tsx
 create mode 100644 app/src/store/themeSlice.test.ts

diff --git a/app/src/components/settings/panels/AppearancePanel.test.tsx b/app/src/components/settings/panels/AppearancePanel.test.tsx
new file mode 100644
index 000000000..16de804c5
--- /dev/null
+++ b/app/src/components/settings/panels/AppearancePanel.test.tsx
@@ -0,0 +1,48 @@
+import { fireEvent, within } from '@testing-library/react';
+import { describe, expect, it, vi } from 'vitest';
+
+import { renderWithProviders } from '../../../test/test-utils';
+import AppearancePanel from './AppearancePanel';
+
+// Pass-through translator so assertions can target the i18n keys directly.
+vi.mock('../../../lib/i18n/I18nContext', () => ({ useT: () => ({ t: (key: string) => key }) }));
+
+vi.mock('../hooks/useSettingsNavigation', () => ({
+  useSettingsNavigation: () => ({ breadcrumbs: [], navigateBack: vi.fn() }),
+}));
+
+vi.mock('../components/SettingsHeader', () => ({
+  default: ({ title }: { title: string }) => <h1>{title}</h1>,
+}));
+
+function renderPanel(fontSize: 'small' | 'medium' | 'large' | 'xlarge' = 'medium') {
+  return renderWithProviders(<AppearancePanel />, {
+    preloadedState: { theme: { mode: 'system', tabBarLabels: 'hover', fontSize } },
+  });
+}
+
+describe('<AppearancePanel /> font size', () => {
+  it('renders the four font-size options as a radio group', () => {
+    const { getByRole } = renderPanel();
+    const group = getByRole('radiogroup', { name: 'settings.appearance.fontSizeAria' });
+    const radios = within(group).getAllByRole('radio');
+    expect(radios).toHaveLength(4);
+  });
+
+  it('marks the active font size as checked', () => {
+    const { getByRole } = renderPanel('large');
+    const group = getByRole('radiogroup', { name: 'settings.appearance.fontSizeAria' });
+    const large = within(group).getByRole('radio', { name: /fontSizeLarge/ });
+    expect(large).toHaveAttribute('aria-checked', 'true');
+  });
+
+  it('dispatches setFontSize when an option is clicked', () => {
+    const { getByRole, store } = renderPanel('medium');
+    const group = getByRole('radiogroup', { name: 'settings.appearance.fontSizeAria' });
+    const xlarge = within(group).getByRole('radio', { name: /fontSizeXLarge/ });
+
+    fireEvent.click(xlarge);
+
+    expect(store.getState().theme.fontSize).toBe('xlarge');
+  });
+});
diff --git a/app/src/components/settings/panels/AppearancePanel.tsx b/app/src/components/settings/panels/AppearancePanel.tsx
index 6c4832ba1..ba01337ea 100644
--- a/app/src/components/settings/panels/AppearancePanel.tsx
+++ b/app/src/components/settings/panels/AppearancePanel.tsx
@@ -3,6 +3,8 @@ import type { ReactElement } from 'react';
 import { useT } from '../../../lib/i18n/I18nContext';
 import { useAppDispatch, useAppSelector } from '../../../store/hooks';
 import {
+  type FontSize,
+  setFontSize,
   setTabBarLabels,
   setThemeMode,
   type TabBarLabels,
@@ -18,6 +20,14 @@ interface ModeOption {
   icon: ReactElement;
 }
 
+interface FontSizeOption {
+  id: FontSize;
+  label: string;
+  description: string;
+  /** Sample "A" glyph sized to preview the option inline. */
+  glyphClass: string;
+}
+
 const SunIcon = (
   <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24" aria-hidden>
     <path
@@ -56,6 +66,7 @@ const AppearancePanel = () => {
   const { navigateBack, breadcrumbs } = useSettingsNavigation();
   const dispatch = useAppDispatch();
   const mode = useAppSelector(state => state.theme.mode);
+  const fontSize = useAppSelector(state => state.theme.fontSize);
   const tabBarLabels = useAppSelector(state => state.theme.tabBarLabels);
   const labelsAlwaysVisible = tabBarLabels === 'always';
   const toggleTabBarLabels = () => {
@@ -87,6 +98,33 @@ const AppearancePanel = () => {
     },
   ];
 
+  const FONT_SIZE_OPTIONS: FontSizeOption[] = [
+    {
+      id: 'small',
+      label: t('settings.appearance.fontSizeSmall'),
+      description: t('settings.appearance.fontSizeSmallDesc'),
+      glyphClass: 'text-xs',
+    },
+    {
+      id: 'medium',
+      label: t('settings.appearance.fontSizeMedium'),
+      description: t('settings.appearance.fontSizeMediumDesc'),
+      glyphClass: 'text-sm',
+    },
+    {
+      id: 'large',
+      label: t('settings.appearance.fontSizeLarge'),
+      description: t('settings.appearance.fontSizeLargeDesc'),
+      glyphClass: 'text-base',
+    },
+    {
+      id: 'xlarge',
+      label: t('settings.appearance.fontSizeXLarge'),
+      description: t('settings.appearance.fontSizeXLargeDesc'),
+      glyphClass: 'text-lg',
+    },
+  ];
+
   return (
     <div>
       <SettingsHeader
@@ -161,6 +199,72 @@ const AppearancePanel = () => {
           </p>
         </div>
 
+        <div>
+          <h3 className="text-xs font-semibold uppercase tracking-wider text-neutral-400 dark:text-neutral-500 mb-2 px-1">
+            {t('settings.appearance.fontSizeHeading')}
+          </h3>
+          <div
+            className="bg-white dark:bg-neutral-900 rounded-xl border border-neutral-200 dark:border-neutral-800 overflow-hidden"
+            role="radiogroup"
+            aria-label={t('settings.appearance.fontSizeAria')}>
+            {FONT_SIZE_OPTIONS.map((opt, idx) => {
+              const selected = opt.id === fontSize;
+              return (
+                <button
+                  key={opt.id}
+                  type="button"
+                  role="radio"
+                  aria-checked={selected}
+                  onClick={() => dispatch(setFontSize(opt.id))}
+                  className={`w-full flex items-center gap-3 px-4 py-3 text-left transition-colors focus:outline-none focus-visible:bg-primary-50 dark:bg-primary-500/10 dark:focus-visible:bg-primary-900/30 ${
+                    idx !== 0 ? 'border-t border-neutral-100 dark:border-neutral-800' : ''
+                  } ${
+                    selected
+                      ? 'bg-primary-50 dark:bg-primary-500/10'
+                      : 'hover:bg-neutral-50 dark:hover:bg-neutral-800/60'
+                  }`}>
+                  <span
+                    className={`flex items-center justify-center w-9 h-9 rounded-lg ${
+                      selected
+                        ? 'bg-primary-500 text-white'
+                        : 'bg-neutral-100 dark:bg-neutral-800 text-neutral-600 dark:text-neutral-300'
+                    }`}>
+                    <span className={`font-semibold leading-none ${opt.glyphClass}`} aria-hidden>
+                      A
+                    </span>
+                  </span>
+                  <span className="flex-1 min-w-0">
+                    <span className="block text-sm font-medium text-neutral-900 dark:text-neutral-100">
+                      {opt.label}
+                    </span>
+                    <span className="block text-xs text-neutral-500 dark:text-neutral-400">
+                      {opt.description}
+                    </span>
+                  </span>
+                  {selected && (
+                    <svg
+                      className="w-5 h-5 text-primary-500"
+                      fill="none"
+                      stroke="currentColor"
+                      viewBox="0 0 24 24"
+                      aria-hidden>
+                      <path
+                        strokeLinecap="round"
+                        strokeLinejoin="round"
+                        strokeWidth={2}
+                        d="M5 13l4 4L19 7"
+                      />
+                    </svg>
+                  )}
+                </button>
+              );
+            })}
+          </div>
+          <p className="text-xs text-neutral-500 dark:text-neutral-400 leading-relaxed px-1 mt-2">
+            {t('settings.appearance.fontSizeHelperText')}
+          </p>
+        </div>
+
         <div>
           <h3 className="text-xs font-semibold uppercase tracking-wider text-neutral-400 dark:text-neutral-500 mb-2 px-1">
             {t('settings.appearance.tabBarHeading')}
diff --git a/app/src/lib/i18n/ar.ts b/app/src/lib/i18n/ar.ts
index 0074c12a5..9879f800b 100644
--- a/app/src/lib/i18n/ar.ts
+++ b/app/src/lib/i18n/ar.ts
@@ -3765,6 +3765,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'اتبع إعداد مظهر نظام التشغيل لديك.',
   'settings.appearance.helperText':
     'يعمل الوضع الداكن على تحويل التطبيق بأكمله - الدردشة والإعدادات واللوحات - إلى لوحة معتمة. "نظام المطابقة" يتتبع مظهر نظام التشغيل الخاص بك وتحديثاته مباشرة.',
+  'settings.appearance.fontSizeHeading': 'حجم الخط',
+  'settings.appearance.fontSizeAria': 'حجم الخط',
+  'settings.appearance.fontSizeSmall': 'صغير',
+  'settings.appearance.fontSizeSmallDesc': 'نص مضغوط — لعرض المزيد على الشاشة.',
+  'settings.appearance.fontSizeMedium': 'متوسط',
+  'settings.appearance.fontSizeMediumDesc': 'الحجم الافتراضي المتوازن.',
+  'settings.appearance.fontSizeLarge': 'كبير',
+  'settings.appearance.fontSizeLargeDesc': 'نص أكبر لقراءة أسهل.',
+  'settings.appearance.fontSizeXLarge': 'كبير جدًا',
+  'settings.appearance.fontSizeXLargeDesc': 'أكبر حجم للنص لأقصى قدر من الوضوح.',
+  'settings.appearance.fontSizeHelperText':
+    'يضبط حجم النص في التطبيق بأكمله — المحادثة والإعدادات واللوحات — بشكل مستقل عن إعداد خط نظامك.',
   'settings.appearance.tabBarHeading': 'شريط علامات التبويب السفلي',
   'settings.appearance.tabBarAlwaysShowLabels': 'إظهار التسميات دائمًا',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/bn.ts b/app/src/lib/i18n/bn.ts
index 8feb8c607..bf550d9ad 100644
--- a/app/src/lib/i18n/bn.ts
+++ b/app/src/lib/i18n/bn.ts
@@ -3838,6 +3838,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'আপনার OS চেহারা সেটিং অনুসরণ করুন.',
   'settings.appearance.helperText':
     'ডার্ক মোড পুরো অ্যাপকে স্যুইচ করে — চ্যাট, সেটিংস, প্যানেল — একটি আবছা প্যালেটে। "ম্যাচ সিস্টেম" আপনার OS চেহারা অনুসরণ করে এবং লাইভ আপডেট করে।',
+  'settings.appearance.fontSizeHeading': 'ফন্টের আকার',
+  'settings.appearance.fontSizeAria': 'ফন্টের আকার',
+  'settings.appearance.fontSizeSmall': 'ছোট',
+  'settings.appearance.fontSizeSmallDesc': 'কমপ্যাক্ট লেখা — স্ক্রিনে আরও বেশি দেখান।',
+  'settings.appearance.fontSizeMedium': 'মাঝারি',
+  'settings.appearance.fontSizeMediumDesc': 'ডিফল্ট, সুষম আকার।',
+  'settings.appearance.fontSizeLarge': 'বড়',
+  'settings.appearance.fontSizeLargeDesc': 'সহজে পড়ার জন্য বড় লেখা।',
+  'settings.appearance.fontSizeXLarge': 'অতিরিক্ত বড়',
+  'settings.appearance.fontSizeXLargeDesc': 'সর্বাধিক পঠনযোগ্যতার জন্য সবচেয়ে বড় লেখা।',
+  'settings.appearance.fontSizeHelperText':
+    'সিস্টেম ফন্ট সেটিং নির্বিশেষে পুরো অ্যাপ জুড়ে — চ্যাট, সেটিংস ও প্যানেল — লেখার আকার পরিবর্তন করে।',
   'settings.appearance.tabBarHeading': 'নীচের ট্যাব বার',
   'settings.appearance.tabBarAlwaysShowLabels': 'সর্বদা লেবেলগুলি দেখান',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/de.ts b/app/src/lib/i18n/de.ts
index 0fddf74b4..4e79a99be 100644
--- a/app/src/lib/i18n/de.ts
+++ b/app/src/lib/i18n/de.ts
@@ -3940,6 +3940,18 @@ const messages: TranslationMap = {
     'Folgt den Einstellungen für das Erscheinungsbild deines Betriebssystems.',
   'settings.appearance.helperText':
     'Der Dunkelmodus schaltet die gesamte App – Chat, Einstellungen, Bedienfelder – auf eine dunkle Palette um. „Match System“ verfolgt das Erscheinungsbild deines Betriebssystems und aktualisiert es live.',
+  'settings.appearance.fontSizeHeading': 'Schriftgröße',
+  'settings.appearance.fontSizeAria': 'Schriftgröße',
+  'settings.appearance.fontSizeSmall': 'Klein',
+  'settings.appearance.fontSizeSmallDesc': 'Kompakter Text — mehr auf dem Bildschirm.',
+  'settings.appearance.fontSizeMedium': 'Mittel',
+  'settings.appearance.fontSizeMediumDesc': 'Die ausgewogene Standardgröße.',
+  'settings.appearance.fontSizeLarge': 'Groß',
+  'settings.appearance.fontSizeLargeDesc': 'Größerer Text für leichteres Lesen.',
+  'settings.appearance.fontSizeXLarge': 'Sehr groß',
+  'settings.appearance.fontSizeXLargeDesc': 'Der größte Text für maximale Lesbarkeit.',
+  'settings.appearance.fontSizeHelperText':
+    'Skaliert den Text in der gesamten App — Chat, Einstellungen und Bereiche — unabhängig von der Schrifteinstellung deines Systems.',
   'settings.appearance.tabBarHeading': 'Untere Tab-Leiste',
   'settings.appearance.tabBarAlwaysShowLabels': 'Beschriftungen immer anzeigen',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/en.ts b/app/src/lib/i18n/en.ts
index f5e80b0c0..d13b210c2 100644
--- a/app/src/lib/i18n/en.ts
+++ b/app/src/lib/i18n/en.ts
@@ -4256,6 +4256,18 @@ const en: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'Follow your OS appearance setting.',
   'settings.appearance.helperText':
     'Dark mode switches the entire app — chat, settings, panels — to a dim palette. "Match system" follows your OS appearance and updates live.',
+  'settings.appearance.fontSizeHeading': 'Font size',
+  'settings.appearance.fontSizeAria': 'Font size',
+  'settings.appearance.fontSizeSmall': 'Small',
+  'settings.appearance.fontSizeSmallDesc': 'Compact text — fit more on screen.',
+  'settings.appearance.fontSizeMedium': 'Medium',
+  'settings.appearance.fontSizeMediumDesc': 'The default, balanced size.',
+  'settings.appearance.fontSizeLarge': 'Large',
+  'settings.appearance.fontSizeLargeDesc': 'Bigger text for easier reading.',
+  'settings.appearance.fontSizeXLarge': 'Extra large',
+  'settings.appearance.fontSizeXLargeDesc': 'The largest text, for maximum readability.',
+  'settings.appearance.fontSizeHelperText':
+    'Scales text across the whole app — chat, settings and panels — independently of your system font setting.',
   'settings.appearance.tabBarHeading': 'Bottom tab bar',
   'settings.appearance.tabBarAlwaysShowLabels': 'Always show labels',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/es.ts b/app/src/lib/i18n/es.ts
index 4f11eb404..152e12f5f 100644
--- a/app/src/lib/i18n/es.ts
+++ b/app/src/lib/i18n/es.ts
@@ -3916,6 +3916,18 @@ const messages: TranslationMap = {
     'Siga la configuración de apariencia de su sistema operativo.',
   'settings.appearance.helperText':
     'El modo oscuro cambia toda la aplicación (chat, configuración, paneles) a una paleta tenue. El "sistema de coincidencias" sigue la apariencia de su sistema operativo y se actualiza en vivo.',
+  'settings.appearance.fontSizeHeading': 'Tamaño de fuente',
+  'settings.appearance.fontSizeAria': 'Tamaño de fuente',
+  'settings.appearance.fontSizeSmall': 'Pequeño',
+  'settings.appearance.fontSizeSmallDesc': 'Texto compacto: más contenido en pantalla.',
+  'settings.appearance.fontSizeMedium': 'Mediano',
+  'settings.appearance.fontSizeMediumDesc': 'El tamaño predeterminado y equilibrado.',
+  'settings.appearance.fontSizeLarge': 'Grande',
+  'settings.appearance.fontSizeLargeDesc': 'Texto más grande para leer con más facilidad.',
+  'settings.appearance.fontSizeXLarge': 'Extra grande',
+  'settings.appearance.fontSizeXLargeDesc': 'El texto más grande, para la máxima legibilidad.',
+  'settings.appearance.fontSizeHelperText':
+    'Escala el texto en toda la app —chat, ajustes y paneles— independientemente de la configuración de fuente de tu sistema.',
   'settings.appearance.tabBarHeading': 'Barra de pestañas inferior',
   'settings.appearance.tabBarAlwaysShowLabels': 'Mostrar siempre etiquetas',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/fr.ts b/app/src/lib/i18n/fr.ts
index a1132594a..a4cd5b8ca 100644
--- a/app/src/lib/i18n/fr.ts
+++ b/app/src/lib/i18n/fr.ts
@@ -3928,6 +3928,18 @@ const messages: TranslationMap = {
     "Suivez les paramètres d'apparence de votre système d'exploitation.",
   'settings.appearance.helperText':
     "Le mode sombre fait basculer l'ensemble de l'application (chat, paramètres, panneaux) vers une palette sombre. \"Match system\" suit l'apparence de votre système d'exploitation et se met à jour en direct.",
+  'settings.appearance.fontSizeHeading': 'Taille de police',
+  'settings.appearance.fontSizeAria': 'Taille de police',
+  'settings.appearance.fontSizeSmall': 'Petite',
+  'settings.appearance.fontSizeSmallDesc': 'Texte compact — plus de contenu à l’écran.',
+  'settings.appearance.fontSizeMedium': 'Moyenne',
+  'settings.appearance.fontSizeMediumDesc': 'La taille par défaut, équilibrée.',
+  'settings.appearance.fontSizeLarge': 'Grande',
+  'settings.appearance.fontSizeLargeDesc': 'Texte plus grand pour une lecture plus facile.',
+  'settings.appearance.fontSizeXLarge': 'Très grande',
+  'settings.appearance.fontSizeXLargeDesc': 'Le texte le plus grand, pour une lisibilité maximale.',
+  'settings.appearance.fontSizeHelperText':
+    'Ajuste la taille du texte dans toute l’application — chat, paramètres et panneaux — indépendamment du réglage de police de votre système.',
   'settings.appearance.tabBarHeading': "Barre d'onglets inférieure",
   'settings.appearance.tabBarAlwaysShowLabels': 'Toujours afficher les étiquettes',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/hi.ts b/app/src/lib/i18n/hi.ts
index 0c0c59654..afa649e18 100644
--- a/app/src/lib/i18n/hi.ts
+++ b/app/src/lib/i18n/hi.ts
@@ -3847,6 +3847,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'अपने OS उपस्थिति सेटिंग का पालन करें.',
   'settings.appearance.helperText':
     'डार्क मोड पूरे ऐप - चैट, सेटिंग्स, पैनल - को एक मंद पैलेट में बदल देता है। "मैच सिस्टम" आपके ओएस की उपस्थिति और अपडेट का लाइव अनुसरण करता है।',
+  'settings.appearance.fontSizeHeading': 'फ़ॉन्ट आकार',
+  'settings.appearance.fontSizeAria': 'फ़ॉन्ट आकार',
+  'settings.appearance.fontSizeSmall': 'छोटा',
+  'settings.appearance.fontSizeSmallDesc': 'संक्षिप्त टेक्स्ट — स्क्रीन पर अधिक दिखाएँ।',
+  'settings.appearance.fontSizeMedium': 'मध्यम',
+  'settings.appearance.fontSizeMediumDesc': 'डिफ़ॉल्ट, संतुलित आकार।',
+  'settings.appearance.fontSizeLarge': 'बड़ा',
+  'settings.appearance.fontSizeLargeDesc': 'आसान पढ़ने के लिए बड़ा टेक्स्ट।',
+  'settings.appearance.fontSizeXLarge': 'बहुत बड़ा',
+  'settings.appearance.fontSizeXLargeDesc': 'अधिकतम पठनीयता के लिए सबसे बड़ा टेक्स्ट।',
+  'settings.appearance.fontSizeHelperText':
+    'आपके सिस्टम फ़ॉन्ट सेटिंग से स्वतंत्र रूप से पूरे ऐप — चैट, सेटिंग्स और पैनल — में टेक्स्ट का आकार बदलता है।',
   'settings.appearance.tabBarHeading': 'निचला टैब बार',
   'settings.appearance.tabBarAlwaysShowLabels': 'हमेशा लेबल दिखाएं',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/id.ts b/app/src/lib/i18n/id.ts
index 876749006..1a938ce62 100644
--- a/app/src/lib/i18n/id.ts
+++ b/app/src/lib/i18n/id.ts
@@ -3854,6 +3854,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'Ikuti pengaturan tampilan OS Anda.',
   'settings.appearance.helperText':
     'Mode gelap mengubah seluruh aplikasi - obrolan, pengaturan, dan panel - ke palet redup. "Ikuti sistem" mengikuti tampilan OS Anda dan diperbarui otomatis.',
+  'settings.appearance.fontSizeHeading': 'Ukuran font',
+  'settings.appearance.fontSizeAria': 'Ukuran font',
+  'settings.appearance.fontSizeSmall': 'Kecil',
+  'settings.appearance.fontSizeSmallDesc': 'Teks ringkas — tampilkan lebih banyak di layar.',
+  'settings.appearance.fontSizeMedium': 'Sedang',
+  'settings.appearance.fontSizeMediumDesc': 'Ukuran default yang seimbang.',
+  'settings.appearance.fontSizeLarge': 'Besar',
+  'settings.appearance.fontSizeLargeDesc': 'Teks lebih besar agar lebih mudah dibaca.',
+  'settings.appearance.fontSizeXLarge': 'Sangat besar',
+  'settings.appearance.fontSizeXLargeDesc': 'Teks terbesar untuk keterbacaan maksimal.',
+  'settings.appearance.fontSizeHelperText':
+    'Menskalakan teks di seluruh aplikasi — obrolan, pengaturan, dan panel — terlepas dari pengaturan font sistem Anda.',
   'settings.appearance.tabBarHeading': 'Bilah tab bawah',
   'settings.appearance.tabBarAlwaysShowLabels': 'Selalu tampilkan label',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/it.ts b/app/src/lib/i18n/it.ts
index 5d32c4ec7..4e2323f00 100644
--- a/app/src/lib/i18n/it.ts
+++ b/app/src/lib/i18n/it.ts
@@ -3905,6 +3905,18 @@ const messages: TranslationMap = {
     "Segui l'impostazione dell'aspetto del tuo sistema operativo.",
   'settings.appearance.helperText':
     'La modalità oscura trasforma l\'intera app (chat, impostazioni, pannelli) in una tavolozza scura. Il "sistema di corrispondenza" segue l\'aspetto del tuo sistema operativo e si aggiorna in tempo reale.',
+  'settings.appearance.fontSizeHeading': 'Dimensione del carattere',
+  'settings.appearance.fontSizeAria': 'Dimensione del carattere',
+  'settings.appearance.fontSizeSmall': 'Piccolo',
+  'settings.appearance.fontSizeSmallDesc': 'Testo compatto — più contenuti sullo schermo.',
+  'settings.appearance.fontSizeMedium': 'Medio',
+  'settings.appearance.fontSizeMediumDesc': 'La dimensione predefinita ed equilibrata.',
+  'settings.appearance.fontSizeLarge': 'Grande',
+  'settings.appearance.fontSizeLargeDesc': 'Testo più grande per una lettura più facile.',
+  'settings.appearance.fontSizeXLarge': 'Molto grande',
+  'settings.appearance.fontSizeXLargeDesc': 'Il testo più grande, per la massima leggibilità.',
+  'settings.appearance.fontSizeHelperText':
+    'Ridimensiona il testo in tutta l’app — chat, impostazioni e pannelli — indipendentemente dall’impostazione del carattere del sistema.',
   'settings.appearance.tabBarHeading': 'Barra delle schede inferiore',
   'settings.appearance.tabBarAlwaysShowLabels': 'Mostra sempre le etichette',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/ko.ts b/app/src/lib/i18n/ko.ts
index 996be46b5..c0a66bc54 100644
--- a/app/src/lib/i18n/ko.ts
+++ b/app/src/lib/i18n/ko.ts
@@ -3799,6 +3799,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'OS 외관 설정을 따릅니다.',
   'settings.appearance.helperText':
     '다크 모드는 전체 앱 — 채팅, 설정, 패널 — 을 어두운 팔레트로 전환합니다. "시스템과 일치"는 OS 외관을 따르며 실시간으로 업데이트됩니다.',
+  'settings.appearance.fontSizeHeading': '글꼴 크기',
+  'settings.appearance.fontSizeAria': '글꼴 크기',
+  'settings.appearance.fontSizeSmall': '작게',
+  'settings.appearance.fontSizeSmallDesc': '간결한 텍스트 — 화면에 더 많이 표시.',
+  'settings.appearance.fontSizeMedium': '보통',
+  'settings.appearance.fontSizeMediumDesc': '기본의 균형 잡힌 크기.',
+  'settings.appearance.fontSizeLarge': '크게',
+  'settings.appearance.fontSizeLargeDesc': '읽기 쉬운 더 큰 텍스트.',
+  'settings.appearance.fontSizeXLarge': '아주 크게',
+  'settings.appearance.fontSizeXLargeDesc': '최대 가독성을 위한 가장 큰 텍스트.',
+  'settings.appearance.fontSizeHelperText':
+    '시스템 글꼴 설정과 관계없이 앱 전체 — 채팅, 설정, 패널 — 의 텍스트 크기를 조정합니다.',
   'settings.appearance.tabBarHeading': '하단 탭 표시줄',
   'settings.appearance.tabBarAlwaysShowLabels': '항상 레이블 표시',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/pl.ts b/app/src/lib/i18n/pl.ts
index ca1e4035f..118127121 100644
--- a/app/src/lib/i18n/pl.ts
+++ b/app/src/lib/i18n/pl.ts
@@ -3907,6 +3907,18 @@ const messages: TranslationMap = {
     'Postępuj zgodnie z ustawieniem wyglądu Twojego systemu operacyjnego.',
   'settings.appearance.helperText':
     'Tryb ciemny przełącza całą aplikację — czat, ustawienia, panele — na przyciemnioną paletę. „Dopasuj do systemu” podąża za wyglądem systemu i aktualizuje się na żywo.',
+  'settings.appearance.fontSizeHeading': 'Rozmiar czcionki',
+  'settings.appearance.fontSizeAria': 'Rozmiar czcionki',
+  'settings.appearance.fontSizeSmall': 'Mały',
+  'settings.appearance.fontSizeSmallDesc': 'Zwarty tekst — więcej na ekranie.',
+  'settings.appearance.fontSizeMedium': 'Średni',
+  'settings.appearance.fontSizeMediumDesc': 'Domyślny, zrównoważony rozmiar.',
+  'settings.appearance.fontSizeLarge': 'Duży',
+  'settings.appearance.fontSizeLargeDesc': 'Większy tekst dla łatwiejszego czytania.',
+  'settings.appearance.fontSizeXLarge': 'Bardzo duży',
+  'settings.appearance.fontSizeXLargeDesc': 'Największy tekst dla maksymalnej czytelności.',
+  'settings.appearance.fontSizeHelperText':
+    'Skaluje tekst w całej aplikacji — czat, ustawienia i panele — niezależnie od ustawienia czcionki w systemie.',
   'settings.appearance.tabBarHeading': 'Dolny pasek zakładek',
   'settings.appearance.tabBarAlwaysShowLabels': 'Zawsze pokazuj etykiety',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/pt.ts b/app/src/lib/i18n/pt.ts
index fb580a19a..d723ade7e 100644
--- a/app/src/lib/i18n/pt.ts
+++ b/app/src/lib/i18n/pt.ts
@@ -3908,6 +3908,18 @@ const messages: TranslationMap = {
     'Siga a configuração de aparência do seu sistema operacional.',
   'settings.appearance.helperText':
     'O modo escuro muda todo o aplicativo – bate-papo, configurações, painéis – para uma paleta escura. "Match system" segue a aparência do seu sistema operacional e atualiza ao vivo.',
+  'settings.appearance.fontSizeHeading': 'Tamanho da fonte',
+  'settings.appearance.fontSizeAria': 'Tamanho da fonte',
+  'settings.appearance.fontSizeSmall': 'Pequeno',
+  'settings.appearance.fontSizeSmallDesc': 'Texto compacto — mais conteúdo na tela.',
+  'settings.appearance.fontSizeMedium': 'Médio',
+  'settings.appearance.fontSizeMediumDesc': 'O tamanho padrão e equilibrado.',
+  'settings.appearance.fontSizeLarge': 'Grande',
+  'settings.appearance.fontSizeLargeDesc': 'Texto maior para leitura mais fácil.',
+  'settings.appearance.fontSizeXLarge': 'Extra grande',
+  'settings.appearance.fontSizeXLargeDesc': 'O maior texto, para máxima legibilidade.',
+  'settings.appearance.fontSizeHelperText':
+    'Dimensiona o texto em todo o app — chat, configurações e painéis — independentemente da configuração de fonte do seu sistema.',
   'settings.appearance.tabBarHeading': 'Barra inferior da guia',
   'settings.appearance.tabBarAlwaysShowLabels': 'Sempre mostrar rótulos',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/ru.ts b/app/src/lib/i18n/ru.ts
index b4b856d64..52a3e158a 100644
--- a/app/src/lib/i18n/ru.ts
+++ b/app/src/lib/i18n/ru.ts
@@ -3873,6 +3873,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': 'Следуйте настройкам внешнего вида вашей ОС.',
   'settings.appearance.helperText':
     'Темный режим переключает все приложение — чат, настройки, панели — на тусклую палитру. «Система сопоставления» следит за внешним видом вашей ОС и обновляет ее в реальном времени.',
+  'settings.appearance.fontSizeHeading': 'Размер шрифта',
+  'settings.appearance.fontSizeAria': 'Размер шрифта',
+  'settings.appearance.fontSizeSmall': 'Маленький',
+  'settings.appearance.fontSizeSmallDesc': 'Компактный текст — больше на экране.',
+  'settings.appearance.fontSizeMedium': 'Средний',
+  'settings.appearance.fontSizeMediumDesc': 'Стандартный сбалансированный размер.',
+  'settings.appearance.fontSizeLarge': 'Большой',
+  'settings.appearance.fontSizeLargeDesc': 'Более крупный текст для удобного чтения.',
+  'settings.appearance.fontSizeXLarge': 'Очень большой',
+  'settings.appearance.fontSizeXLargeDesc': 'Самый крупный текст для максимальной читаемости.',
+  'settings.appearance.fontSizeHelperText':
+    'Масштабирует текст во всём приложении — чат, настройки и панели — независимо от системных настроек шрифта.',
   'settings.appearance.tabBarHeading': 'Нижняя панель вкладок',
   'settings.appearance.tabBarAlwaysShowLabels': 'Всегда показывать метки',
   'settings.appearance.tabBarAlwaysShowLabelsDesc':
diff --git a/app/src/lib/i18n/zh-CN.ts b/app/src/lib/i18n/zh-CN.ts
index 99e49c709..9c2f4c4f0 100644
--- a/app/src/lib/i18n/zh-CN.ts
+++ b/app/src/lib/i18n/zh-CN.ts
@@ -3656,6 +3656,18 @@ const messages: TranslationMap = {
   'settings.appearance.modeSystemDesc': '跟随操作系统外观设置。',
   'settings.appearance.helperText':
     '深色模式会将整个应用——聊天、设置、面板——切换为暗色调。"跟随系统"会同步你的操作系统外观并实时更新。',
+  'settings.appearance.fontSizeHeading': '字体大小',
+  'settings.appearance.fontSizeAria': '字体大小',
+  'settings.appearance.fontSizeSmall': '小',
+  'settings.appearance.fontSizeSmallDesc': '紧凑文字——屏幕显示更多内容。',
+  'settings.appearance.fontSizeMedium': '中',
+  'settings.appearance.fontSizeMediumDesc': '默认的均衡大小。',
+  'settings.appearance.fontSizeLarge': '大',
+  'settings.appearance.fontSizeLargeDesc': '更大的文字，阅读更轻松。',
+  'settings.appearance.fontSizeXLarge': '超大',
+  'settings.appearance.fontSizeXLargeDesc': '最大的文字，可读性最佳。',
+  'settings.appearance.fontSizeHelperText':
+    '在整个应用中缩放文字——聊天、设置和面板——与系统字体设置无关。',
   'settings.appearance.tabBarHeading': '底部标签栏',
   'settings.appearance.tabBarAlwaysShowLabels': '始终显示标签',
   'settings.appearance.tabBarAlwaysShowLabelsDesc': '关闭时，标签仅出现在悬停时或活动选项卡上。',
diff --git a/app/src/providers/ThemeProvider.test.tsx b/app/src/providers/ThemeProvider.test.tsx
new file mode 100644
index 000000000..3d2536834
--- /dev/null
+++ b/app/src/providers/ThemeProvider.test.tsx
@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+
+import { FONT_SIZE_PX, type FontSize } from '../store/themeSlice';
+import { renderWithProviders } from '../test/test-utils';
+import ThemeProvider from './ThemeProvider';
+
+describe('<ThemeProvider />', () => {
+  it.each<FontSize>(['small', 'medium', 'large', 'xlarge'])(
+    'applies the %s font size to the root <html> element',
+    fontSize => {
+      renderWithProviders(
+        <ThemeProvider>
+          <span>child</span>
+        </ThemeProvider>,
+        { preloadedState: { theme: { mode: 'light', tabBarLabels: 'hover', fontSize } } }
+      );
+
+      expect(document.documentElement.style.fontSize).toBe(FONT_SIZE_PX[fontSize]);
+    }
+  );
+
+  it('renders its children', () => {
+    const { getByText } = renderWithProviders(
+      <ThemeProvider>
+        <span>hello</span>
+      </ThemeProvider>,
+      { preloadedState: { theme: { mode: 'light', tabBarLabels: 'hover', fontSize: 'medium' } } }
+    );
+
+    expect(getByText('hello')).toBeInTheDocument();
+  });
+});
diff --git a/app/src/providers/ThemeProvider.tsx b/app/src/providers/ThemeProvider.tsx
index 2f94e1dab..8ba804663 100644
--- a/app/src/providers/ThemeProvider.tsx
+++ b/app/src/providers/ThemeProvider.tsx
@@ -1,18 +1,32 @@
 import { ReactNode, useEffect } from 'react';
 
 import { useAppSelector } from '../store/hooks';
-import { resolveTheme, type ThemeMode } from '../store/themeSlice';
+import { FONT_SIZE_PX, resolveTheme, type ThemeMode } from '../store/themeSlice';
 
 /**
- * Syncs the Redux `theme.mode` slice to the `<html>` element's class list so
- * Tailwind's `darkMode: 'class'` and the `:root.dark` CSS variable block in
- * theme.css activate together.
+ * Syncs the Redux `theme` slice to the root `<html>` element:
  *
- * Mode = `system` also subscribes to `prefers-color-scheme` so OS-level theme
- * flips propagate live without a reload.
+ * - `theme.mode` → the `<html>` class list so Tailwind's `darkMode: 'class'`
+ *   and the `:root.dark` CSS variable block in theme.css activate together.
+ *   Mode = `system` also subscribes to `prefers-color-scheme` so OS-level theme
+ *   flips propagate live without a reload.
+ * - `theme.fontSize` (issue #3120) → the `<html>` inline `font-size`. Because
+ *   Tailwind's text scale is rem-based and `:root` is 16px, scaling the root
+ *   font-size scales every text utility app-wide (chat messages, composer, UI
+ *   chrome) independently of the OS / system font setting.
  */
 const ThemeProvider = ({ children }: { children: ReactNode }) => {
   const mode = useAppSelector(state => state.theme.mode) as ThemeMode;
+  const fontSize = useAppSelector(state => state.theme.fontSize);
+
+  // Apply the global font size to <html>. rem-based Tailwind utilities scale
+  // off this, so a single inline style flows through the whole tree.
+  useEffect(() => {
+    if (typeof document === 'undefined') return;
+    const px = FONT_SIZE_PX[fontSize] ?? FONT_SIZE_PX.medium;
+    console.debug('[theme] applying root font-size', { fontSize, px });
+    document.documentElement.style.fontSize = px;
+  }, [fontSize]);
 
   useEffect(() => {
     const apply = () => {
diff --git a/app/src/store/index.ts b/app/src/store/index.ts
index 8f435c021..98a01a409 100644
--- a/app/src/store/index.ts
+++ b/app/src/store/index.ts
@@ -94,7 +94,7 @@ const persistedLocaleReducer = persistReducer(localePersistConfig, localeReducer
 const themePersistConfig = {
   key: 'theme',
   storage: localStorageAdapter,
-  whitelist: ['mode', 'tabBarLabels'],
+  whitelist: ['mode', 'tabBarLabels', 'fontSize'],
 };
 const persistedThemeReducer = persistReducer(themePersistConfig, themeReducer);
 
diff --git a/app/src/store/themeSlice.test.ts b/app/src/store/themeSlice.test.ts
new file mode 100644
index 000000000..1f2a3af6c
--- /dev/null
+++ b/app/src/store/themeSlice.test.ts
@@ -0,0 +1,41 @@
+import { describe, expect, it } from 'vitest';
+
+import themeReducer, {
+  FONT_SIZE_PX,
+  type FontSize,
+  setFontSize,
+  setTabBarLabels,
+  setThemeMode,
+} from './themeSlice';
+
+describe('themeSlice', () => {
+  it('defaults fontSize to medium', () => {
+    const state = themeReducer(undefined, { type: '@@INIT' });
+    expect(state.fontSize).toBe('medium');
+  });
+
+  it('updates fontSize via setFontSize', () => {
+    let state = themeReducer(undefined, { type: '@@INIT' });
+    state = themeReducer(state, setFontSize('large'));
+    expect(state.fontSize).toBe('large');
+    state = themeReducer(state, setFontSize('small'));
+    expect(state.fontSize).toBe('small');
+  });
+
+  it('leaves mode and tabBarLabels untouched when only fontSize changes', () => {
+    let state = themeReducer(undefined, { type: '@@INIT' });
+    state = themeReducer(state, setThemeMode('dark'));
+    state = themeReducer(state, setTabBarLabels('always'));
+    state = themeReducer(state, setFontSize('xlarge'));
+    expect(state).toEqual({ mode: 'dark', tabBarLabels: 'always', fontSize: 'xlarge' });
+  });
+
+  it('maps every font size to a concrete px value', () => {
+    const sizes: FontSize[] = ['small', 'medium', 'large', 'xlarge'];
+    expect(sizes.map(size => FONT_SIZE_PX[size])).toEqual(['14px', '16px', '18px', '20px']);
+  });
+
+  it('keeps medium aligned with the historical 16px root size', () => {
+    expect(FONT_SIZE_PX.medium).toBe('16px');
+  });
+});
diff --git a/app/src/store/themeSlice.ts b/app/src/store/themeSlice.ts
index c9b41e516..2d843684f 100644
--- a/app/src/store/themeSlice.ts
+++ b/app/src/store/themeSlice.ts
@@ -2,13 +2,33 @@ import { createSlice, type PayloadAction } from '@reduxjs/toolkit';
 
 export type ThemeMode = 'light' | 'dark' | 'system';
 export type TabBarLabels = 'hover' | 'always';
+/**
+ * Global app font size (issue #3120). Drives the root `<html>` font-size, which
+ * scales every rem-based Tailwind text utility — including chat messages and the
+ * composer — independently of the OS / system font setting.
+ */
+export type FontSize = 'small' | 'medium' | 'large' | 'xlarge';
+
+/**
+ * Single source of truth mapping each {@link FontSize} to the concrete root
+ * `font-size` applied to `<html>`. `medium` (16px) matches the historical
+ * `:root` size, so existing users see no change after the field defaults in.
+ * Consumed by `ThemeProvider`; keep this the only place the px values live.
+ */
+export const FONT_SIZE_PX: Record<FontSize, string> = {
+  small: '14px',
+  medium: '16px',
+  large: '18px',
+  xlarge: '20px',
+};
 
 interface ThemeState {
   mode: ThemeMode;
   tabBarLabels: TabBarLabels;
+  fontSize: FontSize;
 }
 
-const initialState: ThemeState = { mode: 'system', tabBarLabels: 'hover' };
+const initialState: ThemeState = { mode: 'system', tabBarLabels: 'hover', fontSize: 'medium' };
 
 const themeSlice = createSlice({
   name: 'theme',
@@ -20,10 +40,13 @@ const themeSlice = createSlice({
     setTabBarLabels(state, action: PayloadAction<TabBarLabels>) {
       state.tabBarLabels = action.payload;
     },
+    setFontSize(state, action: PayloadAction<FontSize>) {
+      state.fontSize = action.payload;
+    },
   },
 });
 
-export const { setThemeMode, setTabBarLabels } = themeSlice.actions;
+export const { setThemeMode, setTabBarLabels, setFontSize } = themeSlice.actions;
 export default themeSlice.reducer;
 
 /**
diff --git a/app/src/test/test-utils.tsx b/app/src/test/test-utils.tsx
index 9f16fe751..ea1c22258 100644
--- a/app/src/test/test-utils.tsx
+++ b/app/src/test/test-utils.tsx
@@ -18,6 +18,7 @@ import localeReducer from '../store/localeSlice';
 import mascotReducer from '../store/mascotSlice';
 import personaReducer from '../store/personaSlice';
 import socketReducer from '../store/socketSlice';
+import themeReducer from '../store/themeSlice';
 
 /**
  * Creates a fresh Redux store for testing.
@@ -27,7 +28,8 @@ import socketReducer from '../store/socketSlice';
  * VoicePanel reads + dispatches against this slice, and useSelector
  * would throw on a missing reducer without a stub here. `persona` is wired
  * in for the same reason (issue #2345): PersonaPanel reads + dispatches
- * against it.
+ * against it. `theme` is wired in for the appearance controls (issue #3120):
+ * AppearancePanel reads + dispatches theme mode, font size and tab-bar labels.
  */
 const testRootReducer = combineReducers({
   channelConnections: channelConnectionsReducer,
@@ -38,6 +40,7 @@ const testRootReducer = combineReducers({
   mascot: mascotReducer,
   persona: personaReducer,
   socket: socketReducer,
+  theme: themeReducer,
 });
 
 export function createTestStore(preloadedState?: Record<string, unknown>) {