diff --git a/scripts/verify-public-target.mjs b/scripts/verify-public-target.mjs
index 439d6c6..aa038c8 100644
--- a/scripts/verify-public-target.mjs
+++ b/scripts/verify-public-target.mjs
@@ -10,7 +10,7 @@ function resolveBaseUrl() {
   }
 
   if (target === 'production' || target === 'prod') {
-    return process.env.PUBLIC_SITE_URL_PROD || process.env.PUBLIC_SITE_URL;
+    return process.env['PUBLIC_SITE_URL_PROD'] || process.env.PUBLIC_SITE_URL;
   }
 
   throw new Error(`Unknown target "${target}". Use "preview" or "production".`);
diff --git a/src/components/SiteHeader.astro b/src/components/SiteHeader.astro
new file mode 100644
index 0000000..f8ea156
--- /dev/null
+++ b/src/components/SiteHeader.astro
@@ -0,0 +1,75 @@
+---
+interface NavItem {
+  href: string;
+  label: string;
+  current?: boolean;
+  attrs?: Record<string, string>;
+  desktopOnly?: boolean;
+}
+
+interface Props {
+  brandHref: string;
+  items: NavItem[];
+  kicker?: string;
+  quickHref?: string;
+  quickLabel?: string;
+  quickAttrs?: Record<string, string>;
+}
+
+const {
+  brandHref,
+  items,
+  kicker = 'Design électronique · Consulting · Formation',
+  quickHref,
+  quickLabel = 'Contact',
+  quickAttrs = {}
+} = Astro.props;
+---
+
+<header class="sticky top-0 z-30 site-nav site-header">
+  <div class="site-shell site-header-shell">
+    <a href={brandHref} class="site-header-brand figma-lab-nav-title">
+      <span class="site-header-brand-title">L'électron rare</span>
+      <span class="site-header-brand-kicker figma-lab-nav-kicker">{kicker}</span>
+    </a>
+
+    <div class="site-header-right">
+      {
+        quickHref && (
+          <a href={quickHref} class="site-header-quick-link figma-lab-nav-link site-navlink" {...quickAttrs}>
+            {quickLabel}
+          </a>
+        )
+      }
+
+      <details class="site-header-menu" data-nav-menu>
+        <summary class="site-header-menu-toggle" aria-label="Ouvrir la navigation principale">
+          <span class="site-header-menu-label">Menu</span>
+          <span class="site-header-menu-icon" aria-hidden="true">
+            <span></span>
+            <span></span>
+          </span>
+        </summary>
+
+        <nav class="site-header-primary" aria-label="Navigation principale">
+          <ul class="figma-lab-nav-list site-header-list">
+            {
+              items.map((item) => (
+                <li class:list={['site-header-item', item.desktopOnly && 'site-header-item--desktop-only']}>
+                  <a
+                    href={item.href}
+                    class:list={['figma-lab-nav-link', 'site-navlink', item.current && 'is-active']}
+                    aria-current={item.current ? 'page' : undefined}
+                    {...(item.attrs ?? {})}
+                  >
+                    {item.label}
+                  </a>
+                </li>
+              ))
+            }
+          </ul>
+        </nav>
+      </details>
+    </div>
+  </div>
+</header>
diff --git a/src/layouts/BaseLayout.astro b/src/layouts/BaseLayout.astro
index 7180404..1378b70 100644
--- a/src/layouts/BaseLayout.astro
+++ b/src/layouts/BaseLayout.astro
@@ -531,6 +531,75 @@ const structuredDataJsonLd = JSON.stringify({
       })();
     </script>
 
+    <script is:inline>
+      (function () {
+        var menus = Array.prototype.slice.call(document.querySelectorAll('[data-nav-menu]'));
+        if (!menus.length) {
+          return;
+        }
+
+        var syncMenuState = function (menu) {
+          var summary = menu.querySelector('summary');
+          if (!summary) {
+            return;
+          }
+          summary.setAttribute('aria-expanded', menu.hasAttribute('open') ? 'true' : 'false');
+        };
+
+        var closeMenu = function (menu) {
+          if (!menu.hasAttribute('open')) {
+            return;
+          }
+          menu.removeAttribute('open');
+          syncMenuState(menu);
+        };
+
+        for (var i = 0; i < menus.length; i += 1) {
+          var menu = menus[i];
+          syncMenuState(menu);
+
+          menu.addEventListener('toggle', function () {
+            syncMenuState(this);
+          });
+
+          var links = menu.querySelectorAll('a');
+          for (var l = 0; l < links.length; l += 1) {
+            links[l].addEventListener('click', function () {
+              var parentMenu = this.closest('[data-nav-menu]');
+              if (parentMenu) {
+                closeMenu(parentMenu);
+              }
+            });
+          }
+        }
+
+        document.addEventListener('click', function (event) {
+          for (var i = 0; i < menus.length; i += 1) {
+            if (!menus[i].contains(event.target)) {
+              closeMenu(menus[i]);
+            }
+          }
+        });
+
+        document.addEventListener('keydown', function (event) {
+          if (event.key !== 'Escape') {
+            return;
+          }
+          for (var i = 0; i < menus.length; i += 1) {
+            closeMenu(menus[i]);
+          }
+        });
+
+        window.addEventListener('resize', function () {
+          if (window.innerWidth >= 768) {
+            for (var i = 0; i < menus.length; i += 1) {
+              closeMenu(menus[i]);
+            }
+          }
+        });
+      })();
+    </script>
+
     <script is:inline>
       (function () {
         var items = Array.prototype.slice.call(document.querySelectorAll('[data-reveal]'));
diff --git a/src/pages/formation.astro b/src/pages/formation.astro
index bf56e79..3bb1922 100644
--- a/src/pages/formation.astro
+++ b/src/pages/formation.astro
@@ -2,6 +2,7 @@
 import BaseLayout from '@/layouts/BaseLayout.astro';
 import '@/styles/global.css';
 import '@/styles/home-workbench.css';
+import SiteHeader from '@/components/SiteHeader.astro';
 import { withSiteBase } from '@/lib/site';
 import { TRACK_EVENTS, trackAttrs } from '@/lib/tracking';
 
@@ -14,25 +15,16 @@ const formationHref = withSiteBase('/formation/');
 const contactHref = withSiteBase('/#contact');
 const labHref = withSiteBase('/lab/');
 const mentionsHref = withSiteBase('/mentions-legales/');
+const headerItems = [
+  { href: homeAboutHref, label: 'Approche' },
+  { href: homeMissionsHref, label: 'Missions' },
+  { href: formationHref, label: 'Formation', current: true },
+  { href: contactHref, label: 'Contact', desktopOnly: true }
+];
 ---
 
 <BaseLayout title={title} description={description} ogDescription="Formations sur mesure en électronique embarquée : PCB, IoT, automatisme industriel. 1 jour, 3 jours ou programme dédié. Écoles, entreprises, centres de formation.">
-  <header class="sticky top-0 z-30 site-nav">
-    <div class="site-shell figma-lab-nav-row">
-      <a href={homeHref} class="figma-lab-nav-title">
-        <span>L'électron rare</span>
-        <span class="figma-lab-nav-kicker">Design électronique · Consulting · Formation</span>
-      </a>
-      <nav aria-label="Navigation principale">
-        <ul class="figma-lab-nav-list">
-          <li><a href={homeAboutHref} class="figma-lab-nav-link site-navlink">Approche</a></li>
-          <li><a href={homeMissionsHref} class="figma-lab-nav-link site-navlink">Missions</a></li>
-          <li><a href={formationHref} class="figma-lab-nav-link site-navlink is-active" aria-current="page">Formation</a></li>
-          <li><a href={contactHref} class="figma-lab-nav-link site-navlink">Contact</a></li>
-        </ul>
-      </nav>
-    </div>
-  </header>
+  <SiteHeader brandHref={homeHref} items={headerItems} quickHref={contactHref} />
 
   <main id="main-content" class="site-shell studio-structure pb-12 pt-3">
 
diff --git a/src/pages/index.astro b/src/pages/index.astro
index d07b837..e5a8d4e 100644
--- a/src/pages/index.astro
+++ b/src/pages/index.astro
@@ -2,6 +2,7 @@
 import BaseLayout from '@/layouts/BaseLayout.astro';
 import '@/styles/global.css';
 import '@/styles/home-workbench.css';
+import SiteHeader from '@/components/SiteHeader.astro';
 import { Hero } from '@/components/sections/Hero';
 import { About } from '@/components/sections/About';
 import { CaseStudies } from '@/components/sections/CaseStudies';
@@ -14,27 +15,18 @@ import { TRACK_EVENTS, trackAttrs } from '@/lib/tracking';
 const formationHref = withSiteBase('/formation/');
 const labHref = withSiteBase('/lab/');
 const mentionsHref = withSiteBase('/mentions-legales/');
+const headerItems = [
+  { href: '#a-propos', label: 'Approche' },
+  { href: '#graphic-sprints-title', label: 'Missions' },
+  { href: formationHref, label: 'Formation' },
+  { href: labHref, label: 'Lab', attrs: trackAttrs(TRACK_EVENTS.ctaLabInteractifOpen, labHref) },
+  { href: '#faq', label: 'FAQ' },
+  { href: '#contact', label: 'Contact', desktopOnly: true }
+];
 ---
 
 <BaseLayout>
-  <header class="sticky top-0 z-30 site-nav">
-    <div class="site-shell figma-lab-nav-row">
-      <a href="#top" class="figma-lab-nav-title">
-        <span>L'électron rare</span>
-        <span class="figma-lab-nav-kicker">Design électronique · Consulting · Formation</span>
-      </a>
-      <nav aria-label="Navigation principale">
-        <ul class="figma-lab-nav-list">
-          <li><a href="#a-propos" class="figma-lab-nav-link site-navlink">Approche</a></li>
-          <li><a href="#graphic-sprints-title" class="figma-lab-nav-link site-navlink">Missions</a></li>
-          <li><a href={formationHref} class="figma-lab-nav-link site-navlink">Formation</a></li>
-          <li><a href={labHref} class="figma-lab-nav-link site-navlink" {...trackAttrs(TRACK_EVENTS.ctaLabInteractifOpen, labHref)}>Lab</a></li>
-          <li><a href="#faq" class="figma-lab-nav-link site-navlink">FAQ</a></li>
-          <li><a href="#contact" class="figma-lab-nav-link site-navlink">Contact</a></li>
-        </ul>
-      </nav>
-    </div>
-  </header>
+  <SiteHeader brandHref="#top" items={headerItems} quickHref="#contact" />
 
   <main id="main-content" class="site-shell studio-structure pb-12 pt-3">
     <section class="structure-grid structure-grid--hero" data-reveal>
diff --git a/src/pages/mentions-legales.astro b/src/pages/mentions-legales.astro
index bb3ea2b..158ef9b 100644
--- a/src/pages/mentions-legales.astro
+++ b/src/pages/mentions-legales.astro
@@ -2,6 +2,7 @@
 import BaseLayout from '@/layouts/BaseLayout.astro';
 import '@/styles/global.css';
 import '@/styles/home-workbench.css';
+import SiteHeader from '@/components/SiteHeader.astro';
 import { withSiteBase } from '@/lib/site';
 
 const title = "Mentions légales — L'électron rare";
@@ -13,25 +14,16 @@ const formationHref = withSiteBase('/formation/');
 const contactHref = withSiteBase('/#contact');
 const labHref = withSiteBase('/lab/');
 const mentionsHref = withSiteBase('/mentions-legales/');
+const headerItems = [
+  { href: homeAboutHref, label: 'Approche' },
+  { href: homeMissionsHref, label: 'Missions' },
+  { href: formationHref, label: 'Formation' },
+  { href: contactHref, label: 'Contact', desktopOnly: true }
+];
 ---
 
 <BaseLayout title={title} description={description}>
-  <header class="sticky top-0 z-30 site-nav">
-    <div class="site-shell figma-lab-nav-row">
-      <a href={homeHref} class="figma-lab-nav-title">
-        <span>L'électron rare</span>
-        <span class="figma-lab-nav-kicker">Design électronique · Consulting · Formation</span>
-      </a>
-      <nav aria-label="Navigation principale">
-        <ul class="figma-lab-nav-list">
-          <li><a href={homeAboutHref} class="figma-lab-nav-link site-navlink">Approche</a></li>
-          <li><a href={homeMissionsHref} class="figma-lab-nav-link site-navlink">Missions</a></li>
-          <li><a href={formationHref} class="figma-lab-nav-link site-navlink">Formation</a></li>
-          <li><a href={contactHref} class="figma-lab-nav-link site-navlink">Contact</a></li>
-        </ul>
-      </nav>
-    </div>
-  </header>
+  <SiteHeader brandHref={homeHref} items={headerItems} quickHref={contactHref} />
 
   <main id="main-content" class="site-shell studio-structure pb-12 pt-3">
 
diff --git a/src/styles/global.css b/src/styles/global.css
index bc92466..d894085 100644
--- a/src/styles/global.css
+++ b/src/styles/global.css
@@ -5214,3 +5214,351 @@ input.contact-minitel-textarea:focus {
   background: #ffffff;
   color: #0b0a09;
 }
+
+/* Responsive header system */
+.site-header.site-nav {
+  overflow: visible;
+}
+
+.site-header-shell {
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) auto;
+  align-items: center;
+  gap: 0.75rem;
+  min-height: 4rem;
+  padding-top: 0.55rem;
+  padding-bottom: 0.55rem;
+}
+
+.site-header-brand {
+  min-width: 0;
+  display: grid;
+  gap: 0.12rem;
+  text-decoration: none;
+}
+
+.site-header-brand-title {
+  display: block;
+  min-width: 0;
+}
+
+.site-header-brand-kicker {
+  display: block;
+}
+
+.site-header-right {
+  display: flex;
+  align-items: center;
+  justify-self: end;
+  gap: 0.5rem;
+}
+
+.site-header-quick-link {
+  display: none;
+}
+
+.site-header-menu {
+  position: relative;
+}
+
+.site-header-menu > summary {
+  list-style: none;
+}
+
+.site-header-menu > summary::-webkit-details-marker {
+  display: none;
+}
+
+.site-header-menu-toggle {
+  min-height: 2.45rem;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  gap: 0.6rem;
+  padding: 0.45rem 0.88rem;
+  border: 1px solid rgba(125, 99, 77, 0.18);
+  border-radius: 999px;
+  background: rgba(255, 252, 248, 0.92);
+  color: #241912;
+  cursor: pointer;
+  user-select: none;
+  font-family: "IBM Plex Mono", ui-monospace, Menlo, Consolas, monospace;
+  font-size: 0.68rem;
+  font-weight: 600;
+  letter-spacing: 0.1em;
+  text-transform: uppercase;
+  box-shadow: 0 8px 18px rgba(95, 73, 55, 0.08);
+  transition:
+    background-color 0.16s ease,
+    border-color 0.16s ease,
+    box-shadow 0.16s ease,
+    transform 0.16s ease;
+}
+
+.site-header-menu-toggle:hover,
+.site-header-menu-toggle:focus-visible {
+  border-color: rgba(183, 86, 44, 0.34);
+  background: rgba(255, 255, 255, 0.98);
+  box-shadow: 0 12px 24px rgba(95, 73, 55, 0.12);
+  transform: translateY(-1px);
+}
+
+.site-header-menu-label {
+  white-space: nowrap;
+}
+
+.site-header-menu-icon {
+  width: 1rem;
+  height: 0.8rem;
+  display: grid;
+  align-content: center;
+  gap: 0.22rem;
+}
+
+.site-header-menu-icon span {
+  display: block;
+  width: 100%;
+  height: 2px;
+  border-radius: 999px;
+  background: currentColor;
+  transition:
+    transform 0.18s ease,
+    opacity 0.18s ease;
+}
+
+.site-header-menu[open] .site-header-menu-icon span:first-child {
+  transform: translateY(4px) rotate(45deg);
+}
+
+.site-header-menu[open] .site-header-menu-icon span:last-child {
+  transform: translateY(-4px) rotate(-45deg);
+}
+
+.site-header-primary {
+  display: none;
+}
+
+.site-header-menu[open] .site-header-primary {
+  display: block;
+}
+
+.site-header-primary {
+  position: absolute;
+  top: calc(100% + 0.65rem);
+  right: 0;
+  width: min(22rem, calc(100vw - 1rem));
+  padding: 0.72rem;
+  border: 1px solid rgba(123, 97, 74, 0.16);
+  border-radius: 1rem;
+  background:
+    linear-gradient(180deg, rgba(255, 252, 247, 0.98), rgba(244, 235, 224, 0.96)),
+    linear-gradient(135deg, rgba(183, 86, 44, 0.06), transparent 42%);
+  box-shadow:
+    0 24px 48px rgba(95, 73, 55, 0.16),
+    inset 0 1px 0 rgba(255, 255, 255, 0.55);
+  backdrop-filter: blur(18px);
+}
+
+.site-header-list {
+  margin: 0;
+  padding: 0;
+  list-style: none;
+  display: grid;
+  gap: 0.5rem;
+}
+
+.site-header-list .figma-lab-nav-link,
+.site-header-list .site-navlink {
+  width: 100%;
+  justify-content: flex-start;
+}
+
+.site-header-item--desktop-only {
+  display: none;
+}
+
+.site-nav.is-compact .site-header-shell {
+  min-height: 3.5rem;
+  padding-top: 0.38rem;
+  padding-bottom: 0.38rem;
+}
+
+@media (min-width: 768px) {
+  .site-header-shell {
+    grid-template-columns: minmax(0, auto) 1fr;
+    gap: 1rem;
+    min-height: 4.15rem;
+  }
+
+  .site-header-right {
+    min-width: 0;
+    width: 100%;
+  }
+
+  .site-header-menu {
+    width: 100%;
+  }
+
+  .site-header-menu-toggle {
+    display: none;
+  }
+
+  .site-header-primary {
+    position: static;
+    display: block;
+    width: auto;
+    padding: 0;
+    border: 0;
+    border-radius: 0;
+    background: none;
+    box-shadow: none;
+    backdrop-filter: none;
+  }
+
+  .site-header-list {
+    display: flex;
+    flex-wrap: wrap;
+    justify-content: flex-end;
+    gap: 0.65rem;
+  }
+
+  .site-header-list .figma-lab-nav-link,
+  .site-header-list .site-navlink {
+    width: auto;
+    justify-content: center;
+  }
+
+  .site-header-item--desktop-only {
+    display: list-item;
+  }
+}
+
+@media (max-width: 767px) {
+  .site-header-shell {
+    min-height: 3.35rem;
+    gap: 0.55rem;
+    padding-top: 0.42rem;
+    padding-bottom: 0.42rem;
+  }
+
+  .site-header-brand {
+    gap: 0;
+  }
+
+  .site-header-brand-title {
+    max-width: 100%;
+    font-size: 1rem;
+    line-height: 1.02;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+  }
+
+  .site-header-brand-kicker {
+    display: none;
+  }
+
+  .site-header-right {
+    gap: 0.42rem;
+  }
+
+  .site-header-quick-link {
+    min-height: 2.45rem;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding-inline: 0.82rem;
+    font-size: 0.66rem;
+    letter-spacing: 0.08em;
+    white-space: nowrap;
+  }
+
+  .site-header-menu-toggle {
+    padding-inline: 0.78rem;
+  }
+
+  .site-header-primary {
+    max-height: min(74vh, 28rem);
+    overflow: auto;
+    -webkit-overflow-scrolling: touch;
+  }
+
+  .site-header-list .figma-lab-nav-link,
+  .site-header-list .site-navlink {
+    min-height: 2.75rem;
+    padding-inline: 0.95rem;
+    font-size: 0.69rem;
+  }
+}
+
+@media (max-width: 420px) {
+  .site-header-shell {
+    grid-template-columns: minmax(0, 1fr);
+  }
+
+  .site-header-right {
+    width: 100%;
+    justify-content: stretch;
+  }
+
+  .site-header-quick-link,
+  .site-header-menu {
+    flex: 1 1 0;
+  }
+
+  .site-header-quick-link,
+  .site-header-menu-toggle {
+    width: 100%;
+  }
+
+  .site-header-primary {
+    width: 100%;
+    left: 0;
+    right: auto;
+  }
+}
+
+:root[data-da-variant="v12"] .site-header-brand {
+  color: #241912;
+}
+
+:root[data-da-variant="v12"] .site-header-brand-title {
+  font-family: "Fraunces", "Times New Roman", serif;
+  font-size: clamp(1rem, 1.45vw, 1.16rem);
+  font-weight: 700;
+  letter-spacing: 0.01em;
+  text-transform: none;
+}
+
+:root[data-da-variant="v12"] .site-header-brand-kicker {
+  color: #7c6556;
+  font-family: "IBM Plex Mono", ui-monospace, Menlo, Consolas, monospace;
+  font-size: 0.62rem;
+  font-weight: 500;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+}
+
+:root[data-da-variant="v12"][data-theme="high-contrast"] .site-header-menu-toggle {
+  border-color: rgba(15, 15, 15, 0.14);
+  background: rgba(255, 255, 255, 0.92);
+  color: #1e1712;
+  box-shadow: 0 10px 20px rgba(66, 45, 31, 0.08);
+}
+
+:root[data-da-variant="v12"][data-theme="high-contrast"] .site-header-menu-toggle:hover,
+:root[data-da-variant="v12"][data-theme="high-contrast"] .site-header-menu-toggle:focus-visible {
+  border-color: rgba(183, 86, 44, 0.28);
+  background: rgba(255, 255, 255, 1);
+  box-shadow: 0 14px 28px rgba(66, 45, 31, 0.12);
+}
+
+:root[data-da-variant="v12"][data-theme="high-contrast"] .site-header-primary {
+  border-color: rgba(80, 61, 46, 0.14);
+  background:
+    linear-gradient(180deg, rgba(255, 252, 248, 0.99), rgba(246, 239, 231, 0.98)),
+    linear-gradient(135deg, rgba(183, 86, 44, 0.04), transparent 46%);
+  box-shadow:
+    0 26px 52px rgba(87, 63, 44, 0.16),
+    inset 0 1px 0 rgba(255, 255, 255, 0.75);
+}