diff --git a/public/index.html b/public/index.html
index 6667338..39e1fc8 100644
--- a/public/index.html
+++ b/public/index.html
@@ -8,19 +8,26 @@
 <link href="https://fonts.googleapis.com/css2?family=DM+Sans:ital,wght@0,400;0,500;0,600;0,700;1,400&family=Playfair+Display:wght@600;700&display=swap" rel="stylesheet">
 <style>
   *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
+  :root {
+    --font-size: 15px;
+    --title-size: 32px;
+    --calendar-size: 14px;
+    --button-size: 14px;
+  }
   body {
     font-family: 'DM Sans', sans-serif;
     background: #F5F0EB;
     color: #3A332D;
     min-height: 100vh;
     padding: 20px 16px;
+    font-size: var(--font-size);
   }
   .container { max-width: 520px; margin: 0 auto; }
 
   /* Header */
   .header { text-align: center; margin-bottom: 28px; }
-  .header-sub { font-size: 11px; letter-spacing: 0.2em; color: #B0A89E; font-weight: 500; text-transform: uppercase; margin-bottom: 4px; }
-  .header h1 { font-family: 'Playfair Display', serif; font-size: 28px; font-weight: 700; color: #3A332D; line-height: 1.2; }
+  .header-sub { font-size: calc(var(--font-size) - 2px); letter-spacing: 0.2em; color: #B0A89E; font-weight: 500; text-transform: uppercase; margin-bottom: 4px; }
+  .header h1 { font-family: 'Playfair Display', serif; font-size: var(--title-size); font-weight: 700; color: #3A332D; line-height: 1.2; }
   .header-line { width: 40px; height: 2px; background: #C17F59; margin: 10px auto 0; border-radius: 1px; }
 
   /* User bar */
@@ -30,8 +37,8 @@
     background: #FFF; box-shadow: 0 1px 3px rgba(0,0,0,0.04);
   }
   .user-bar-dot { width: 10px; height: 10px; border-radius: 50%; flex-shrink: 0; }
-  .user-bar-name { font-size: 13px; font-weight: 600; color: #3A332D; }
-  .user-bar-label { font-size: 11px; color: #B0A89E; }
+  .user-bar-name { font-size: var(--font-size); font-weight: 600; color: #3A332D; }
+  .user-bar-label { font-size: calc(var(--font-size) - 2px); color: #B0A89E; }
   .btn-logout {
     margin-left: auto; border: none; background: #F5F0EB; border-radius: 6px;
     padding: 4px 10px; font-size: 11px; font-weight: 500; color: #8B7E74;
@@ -41,27 +48,27 @@
 
   /* Cards */
   .card { background: #FFF; border-radius: 14px; padding: 16px; margin-bottom: 14px; box-shadow: 0 1px 3px rgba(0,0,0,0.04); }
-  .card-title { font-size: 11px; font-weight: 600; color: #8B7E74; margin-bottom: 10px; text-transform: uppercase; letter-spacing: 0.08em; }
+  .card-title { font-size: calc(var(--font-size) - 2px); font-weight: 600; color: #8B7E74; margin-bottom: 10px; text-transform: uppercase; letter-spacing: 0.08em; }
 
   /* Controls */
   .controls { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
   .controls select, .controls input {
     padding: 7px 10px; border-radius: 8px; border: 1px solid #E8E0D8;
-    background: #FDFBF9; font-size: 13px; font-family: 'DM Sans', sans-serif;
+    background: #FDFBF9; font-size: var(--button-size); font-family: 'DM Sans', sans-serif;
     color: #3A332D; flex: 1; min-width: 100px;
   }
-  .hint { font-size: 11px; color: #B0A89E; margin-top: 8px; }
+  .hint { font-size: calc(var(--font-size) - 2px); color: #B0A89E; margin-top: 8px; }
 
   /* Calendar */
   .cal-nav { display: flex; justify-content: space-between; align-items: center; margin-bottom: 12px; }
   .cal-nav button {
-    border: none; background: #F5F0EB; border-radius: 8px; width: 32px; height: 32px;
-    cursor: pointer; font-size: 16px; color: #5C524A; display: flex; align-items: center; justify-content: center;
+    border: none; background: #F5F0EB; border-radius: 8px; width: 36px; height: 36px;
+    cursor: pointer; font-size: 18px; color: #5C524A; display: flex; align-items: center; justify-content: center;
   }
   .cal-nav button:hover { background: #EAE3DB; }
-  .cal-month { font-size: 16px; font-weight: 600; color: #3A332D; }
+  .cal-month { font-size: calc(var(--title-size) * 0.55); font-weight: 600; color: #3A332D; }
   .cal-grid { display: grid; grid-template-columns: repeat(7, 1fr); gap: 2px; }
-  .cal-day-header { text-align: center; padding: 6px 0; font-size: 11px; font-weight: 600; color: #8B7E74; letter-spacing: 0.05em; }
+  .cal-day-header { text-align: center; padding: 6px 0; font-size: calc(var(--calendar-size) - 1px); font-weight: 600; color: #8B7E74; letter-spacing: 0.05em; }
   .cal-day {
     position: relative; min-height: 48px; padding: 3px; border-radius: 6px;
     background: #FDFBF9; cursor: pointer; border: 1px solid transparent;
@@ -71,7 +78,7 @@
   .cal-day.empty { background: transparent; cursor: default; }
   .cal-day.today { border: 2px solid #C17F59; }
   .cal-day.in-selection { background: #D4C5B9; }
-  .cal-day-num { font-size: 12px; font-weight: 400; color: #5C524A; text-align: right; padding-right: 2px; display: block; }
+  .cal-day-num { font-size: var(--calendar-size); font-weight: 400; color: #5C524A; text-align: right; padding-right: 2px; display: block; }
   .cal-day.today .cal-day-num { font-weight: 700; color: #C17F59; }
   .cal-day-dots { display: flex; flex-wrap: wrap; gap: 2px; margin-top: 2px; }
   .dot { width: 8px; height: 8px; border-radius: 50%; flex-shrink: 0; }
@@ -79,10 +86,10 @@
 
   /* Legend */
   .legend { display: flex; flex-wrap: wrap; gap: 10px; justify-content: center; margin-bottom: 14px; padding: 8px 0; }
-  .legend-item { display: flex; align-items: center; gap: 5px; font-size: 11px; color: #5C524A; }
+  .legend-item { display: flex; align-items: center; gap: 5px; font-size: calc(var(--font-size) - 2px); color: #5C524A; }
   .legend-dot { width: 8px; height: 8px; border-radius: 50%; }
   .legend-row { width: 100%; display: flex; justify-content: center; gap: 16px; margin-top: 2px; }
-  .legend-row span { font-size: 10px; color: #B0A89E; }
+  .legend-row span { font-size: calc(var(--font-size) - 3px); color: #B0A89E; }
 
   /* Booking list */
   .booking-item {
@@ -91,20 +98,20 @@
   }
   .booking-dot { width: 10px; height: 10px; border-radius: 50%; flex-shrink: 0; }
   .booking-info { flex: 1; min-width: 0; }
-  .booking-name { font-size: 13px; font-weight: 600; color: #3A332D; }
+  .booking-name { font-size: var(--font-size); font-weight: 600; color: #3A332D; }
   .booking-badge {
-    display: inline-block; margin-left: 8px; font-size: 10px; font-weight: 500;
+    display: inline-block; margin-left: 8px; font-size: calc(var(--font-size) - 3px); font-weight: 500;
     padding: 1px 6px; border-radius: 10px;
   }
   .booking-badge.confirmed { background: #81B29A22; color: #5A9A78; }
   .booking-badge.planned { background: #F2CC8F33; color: #C49A4A; }
-  .booking-dates { font-size: 11px; color: #8B7E74; margin-top: 2px; }
+  .booking-dates { font-size: calc(var(--font-size) - 2px); color: #8B7E74; margin-top: 2px; }
   .booking-actions button {
     border: none; background: none; cursor: pointer; font-size: 14px; padding: 4px; border-radius: 4px;
   }
   .booking-actions .toggle { color: #B0A89E; }
   .booking-actions .delete { color: #D4756B; }
-  .empty-state { text-align: center; padding: 30px; color: #B0A89E; font-style: italic; }
+  .empty-state { text-align: center; padding: 30px; color: #B0A89E; font-style: italic; font-size: var(--font-size); }
 
   /* Comments */
   .comments-list { display: flex; flex-direction: column; gap: 8px; margin-bottom: 16px; max-height: 400px; overflow-y: auto; }
@@ -113,9 +120,9 @@
     border-left: 3px solid #ccc; position: relative;
   }
   .comment-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 4px; }
-  .comment-author { font-size: 12px; font-weight: 600; }
-  .comment-time { font-size: 10px; color: #B0A89E; }
-  .comment-text { font-size: 13px; color: #5C524A; line-height: 1.5; }
+  .comment-author { font-size: calc(var(--font-size) - 1px); font-weight: 600; }
+  .comment-time { font-size: calc(var(--font-size) - 3px); color: #B0A89E; }
+  .comment-text { font-size: var(--font-size); color: #5C524A; line-height: 1.5; }
   .comment-delete {
     border: none; background: none; cursor: pointer; font-size: 12px;
     color: #D4756B; padding: 2px 4px; border-radius: 4px; margin-left: 8px;
@@ -125,13 +132,13 @@
   .comment-form { display: flex; gap: 8px; align-items: flex-end; }
   .comment-form input {
     flex: 1; padding: 8px 12px; border-radius: 8px; border: 1px solid #E8E0D8;
-    background: #FFF; font-size: 13px; font-family: 'DM Sans', sans-serif;
+    background: #FFF; font-size: var(--button-size); font-family: 'DM Sans', sans-serif;
     color: #3A332D; outline: none;
   }
   .comment-form input:focus { border-color: #C17F59; }
   .btn-send {
     padding: 8px 16px; border-radius: 8px; border: none;
-    background: #C17F59; color: #FFF; font-size: 12px; font-weight: 600;
+    background: #C17F59; color: #FFF; font-size: var(--button-size); font-weight: 600;
     cursor: pointer; font-family: 'DM Sans', sans-serif; white-space: nowrap;
   }
   .btn-send:hover { background: #A96A4A; }
@@ -144,7 +151,7 @@
   .login-box { text-align: center; width: 280px; }
   .login-box input, .login-box select {
     padding: 10px 16px; border-radius: 8px; border: 1px solid #E8E0D8;
-    font-size: 14px; font-family: 'DM Sans', sans-serif; width: 100%;
+    font-size: var(--button-size); font-family: 'DM Sans', sans-serif; width: 100%;
     margin-bottom: 10px; text-align: center; background: #FFF; color: #3A332D;
   }
   .login-box .btn-send { display: block; width: 100%; padding: 10px; }
@@ -154,7 +161,7 @@
     display: flex; align-items: center; gap: 6px;
     padding: 8px 14px; border-radius: 10px; border: 2px solid #E8E0D8;
     background: #FFF; cursor: pointer; font-family: 'DM Sans', sans-serif;
-    font-size: 13px; font-weight: 500; color: #5C524A; transition: all 0.15s ease;
+    font-size: var(--button-size); font-weight: 500; color: #5C524A; transition: all 0.15s ease;
   }
   .login-member-btn:hover { border-color: #C17F59; }
   .login-member-btn.selected { border-color: #C17F59; background: #FDF6F0; font-weight: 600; }
@@ -167,10 +174,10 @@
 
 <div id="login-screen" class="login-overlay" style="display:none;">
   <div class="login-box">
-    <div class="header-sub">Révfülöp · Balaton</div>
-    <h1 style="font-family:'Playfair Display',serif;font-size:28px;font-weight:700;color:#3A332D;margin:4px 0 8px;">Nyaraló Naptár</h1>
+    <div class="header-sub site-subtitle">Révfülöp · Balaton</div>
+    <h1 class="site-title" style="font-family:'Playfair Display',serif;font-size:var(--title-size);font-weight:700;color:#3A332D;margin:4px 0 8px;">Nyaraló Naptár</h1>
     <div class="header-line" style="margin:0 auto 12px;"></div>
-    <div style="font-size:12px;color:#8B7E74;margin-bottom:4px;">Ki vagy?</div>
+    <div style="font-size:calc(var(--font-size) - 1px);color:#8B7E74;margin-bottom:4px;">Ki vagy?</div>
     <div class="login-members" id="login-members"></div>
     <input type="password" id="login-password" placeholder="Jelszó" onkeydown="if(event.key==='Enter')doLogin()">
     <button class="btn-send" onclick="doLogin()">Belépés</button>
@@ -180,8 +187,8 @@
 
 <div id="app" class="container" style="display:none;">
   <div class="header">
-    <div class="header-sub">Révfülöp · Balaton</div>
-    <h1>Nyaraló Naptár</h1>
+    <div class="header-sub site-subtitle">Révfülöp · Balaton</div>
+    <h1 class="site-title">Nyaraló Naptár</h1>
     <div class="header-line"></div>
   </div>
 
@@ -271,8 +278,28 @@ async function api(method, path, body) {
   return res.json();
 }
 
+// Apply UI config as CSS variables
+async function loadConfig() {
+  try {
+    const config = await fetch('/api/config').then(r => r.json());
+    const root = document.documentElement;
+    root.style.setProperty('--font-size', config.fontSize + 'px');
+    root.style.setProperty('--title-size', config.titleSize + 'px');
+    root.style.setProperty('--calendar-size', config.calendarSize + 'px');
+    root.style.setProperty('--button-size', config.buttonSize + 'px');
+    // Update site name/subtitle if customized
+    document.querySelectorAll('.site-title').forEach(el => el.textContent = config.siteName);
+    document.querySelectorAll('.site-subtitle').forEach(el => el.textContent = config.siteSubtitle);
+  } catch (e) {
+    console.log('Using default UI config');
+  }
+}
+
 // Auth
 async function checkAuth() {
+  // Load UI config first (no auth needed)
+  await loadConfig();
+
   // Always load members first (available without auth)
   members = await fetch('/api/members').then(r => r.json());
   buildLoginMembers();
diff --git a/server.js b/server.js
index 171033a..e537aab 100644
--- a/server.js
+++ b/server.js
@@ -11,7 +11,17 @@ const DB_PATH = process.env.DB_PATH || '/data/revfulop.db';
 const AUTH_PASSWORD = process.env.SIMPLE_AUTH_PASSWORD || '';
 const AUTH_ENABLED = AUTH_PASSWORD.length > 0;
 
-// Family members config (can be overridden via FAMILY_MEMBERS env var as JSON)
+// UI config (all overridable via env vars, no rebuild needed)
+const UI_CONFIG = {
+  fontSize: process.env.UI_FONT_SIZE || '15',           // base font size in px
+  titleSize: process.env.UI_TITLE_SIZE || '32',         // main title size in px
+  calendarSize: process.env.UI_CALENDAR_SIZE || '14',   // calendar day number size in px
+  buttonSize: process.env.UI_BUTTON_SIZE || '14',       // button/input font size in px
+  siteName: process.env.UI_SITE_NAME || 'Nyaraló Naptár',
+  siteSubtitle: process.env.UI_SITE_SUBTITLE || 'Révfülöp · Balaton',
+};
+
+// Family members config (can be overridable via FAMILY_MEMBERS env var as JSON)
 const DEFAULT_MEMBERS = [
   { id: "katinka", name: "Katinka", color: "#513eff" },
   { id: "orsi", name: "Orsi", color: "#a15dd8" },
@@ -122,6 +132,11 @@ app.get('/api/members', (req, res) => {
   res.json(FAMILY_MEMBERS);
 });
 
+// UI config endpoint
+app.get('/api/config', (req, res) => {
+  res.json(UI_CONFIG);
+});
+
 // Bookings CRUD
 app.get('/api/bookings', (req, res) => {
   const bookings = db.prepare('SELECT * FROM bookings ORDER BY start_date').all();
@@ -191,4 +206,5 @@ app.listen(PORT, '0.0.0.0', () => {
   console.log(`Révfülöp Calendar running on port ${PORT}`);
   console.log(`Auth: ${AUTH_ENABLED ? 'ENABLED (simple password)' : 'DISABLED (public access)'}`);
   console.log(`Members: ${FAMILY_MEMBERS.map(m => m.name).join(', ')}`);
+  console.log(`UI: font=${UI_CONFIG.fontSize}px, title=${UI_CONFIG.titleSize}px, calendar=${UI_CONFIG.calendarSize}px`);
 });
\ No newline at end of file