diff --git a/src/App.vue b/src/App.vue
index d23654c..173f838 100644
--- a/src/App.vue
+++ b/src/App.vue
@@ -1,10 +1,17 @@
 <script setup lang="ts">
 import AppShell from './components/AppShell.vue';
 import type { ProductionInputs } from './content/types';
+import './styles/tokens.css';
+import './styles/base.css';
+import './styles/layout.css';
+import './styles/components.css';
+import './styles/print.css';
 
 defineProps<{ inputs: Readonly<ProductionInputs> }>();
 </script>
 
 <template>
-  <AppShell :content="inputs.content" />
+  <div class="portfolio-shell">
+    <AppShell :content="inputs.content" />
+  </div>
 </template>
diff --git a/src/components/AppShell.vue b/src/components/AppShell.vue
index c1cf7fa..e8d26eb 100644
--- a/src/components/AppShell.vue
+++ b/src/components/AppShell.vue
@@ -31,13 +31,13 @@ const canonicalNavigation = computed(() => canonicalSectionIds.map((id) => ({ id
 
 <template>
   <a class="skip-link" href="#portfolio-content">Skip to portfolio content</a>
-  <header>
+  <header class="site-header">
     <h1>{{ content.identity.name }}</h1>
     <p>{{ content.identity.role }}</p>
     <SiteNavigation :items="canonicalNavigation" />
   </header>
 
-  <main id="portfolio-content">
+  <main id="portfolio-content" class="portfolio-main">
     <PortfolioSection id="start" :index="1" :eyebrow="sectionLabel('start').toUpperCase()" :heading="sectionLabel('start').toUpperCase()">
       <p>{{ content.identity.valueProposition }}</p>
     </PortfolioSection>
diff --git a/src/components/PortfolioSection.vue b/src/components/PortfolioSection.vue
index fcda921..8ac7d5f 100644
--- a/src/components/PortfolioSection.vue
+++ b/src/components/PortfolioSection.vue
@@ -8,8 +8,8 @@ defineProps<{
 </script>
 
 <template>
-  <section :id="id" :aria-labelledby="`${id}-heading`" :data-section-index="index">
-    <p>{{ String(index).padStart(2, '0') }} / {{ eyebrow }}</p>
+  <section :id="id" class="portfolio-section" :aria-labelledby="`${id}-heading`" :data-section-index="index">
+    <p class="route-label">{{ String(index).padStart(2, '0') }} / {{ eyebrow }}</p>
     <h2 :id="`${id}-heading`">{{ heading }}</h2>
     <slot />
   </section>
diff --git a/src/components/SiteNavigation.vue b/src/components/SiteNavigation.vue
index f98eb12..dbeb8fe 100644
--- a/src/components/SiteNavigation.vue
+++ b/src/components/SiteNavigation.vue
@@ -5,7 +5,7 @@ defineProps<{ items: ReadonlyArray<{ id: SectionId; label: string }> }>();
 </script>
 
 <template>
-  <nav aria-label="Portfolio sections">
+  <nav class="site-navigation" aria-label="Portfolio sections">
     <ul>
       <li v-for="item in items" :key="item.id">
         <a :href="`#${item.id}`">{{ item.label }}</a>
diff --git a/src/styles/base.css b/src/styles/base.css
new file mode 100644
index 0000000..a4d911b
--- /dev/null
+++ b/src/styles/base.css
@@ -0,0 +1,121 @@
+* {
+  box-sizing: border-box;
+}
+
+html {
+  min-width: 0;
+  background: var(--canvas);
+  color: var(--text);
+  font-family: var(--sans);
+  font-size: 100%;
+  line-height: 1.55;
+  scroll-behavior: auto;
+  text-size-adjust: 100%;
+}
+
+body {
+  min-width: 0;
+  min-height: 100vh;
+  margin: 0;
+  overflow-wrap: anywhere;
+  background: var(--canvas);
+}
+
+button,
+input,
+textarea,
+select {
+  font: inherit;
+}
+
+a {
+  color: var(--cyan);
+  overflow-wrap: anywhere;
+  text-decoration-color: color-mix(in srgb, currentcolor 55%, transparent);
+  text-underline-offset: 0.18em;
+}
+
+a:hover {
+  color: var(--text);
+  text-decoration-color: currentcolor;
+}
+
+a:focus-visible,
+button:focus-visible,
+input:focus-visible,
+textarea:focus-visible,
+select:focus-visible,
+[tabindex]:focus-visible {
+  outline: 3px solid var(--focus);
+  outline-offset: 3px;
+}
+
+::selection {
+  background: var(--amber);
+  color: #14100a;
+}
+
+h1,
+h2,
+h3,
+p,
+dl,
+ul,
+ol,
+figure {
+  margin-block: 0;
+}
+
+h1,
+h2,
+h3 {
+  color: var(--text);
+  font-weight: 680;
+  letter-spacing: -0.025em;
+  line-height: 1.08;
+  text-wrap: balance;
+}
+
+p,
+li,
+dd,
+dt,
+a {
+  max-inline-size: 72ch;
+}
+
+svg,
+img,
+video,
+canvas {
+  display: block;
+  max-inline-size: 100%;
+}
+
+.skip-link {
+  position: fixed;
+  z-index: 10;
+  inset: var(--space-2) auto auto var(--space-2);
+  min-block-size: 44px;
+  padding: var(--space-1) var(--space-2);
+  transform: translateY(-160%);
+  background: var(--amber);
+  color: #171006;
+  font-weight: 700;
+  transition: transform var(--transition);
+}
+
+.skip-link:focus {
+  transform: translateY(0);
+}
+
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    scroll-behavior: auto !important;
+    transition-duration: 0.001s !important;
+    animation-duration: 0.001s !important;
+    animation-iteration-count: 1 !important;
+  }
+}
diff --git a/src/styles/components.css b/src/styles/components.css
new file mode 100644
index 0000000..43b9c06
--- /dev/null
+++ b/src/styles/components.css
@@ -0,0 +1,131 @@
+.route-label {
+  color: var(--cyan);
+  font-family: var(--mono);
+  font-size: var(--step--1);
+  font-weight: 650;
+  letter-spacing: 0.08em;
+  line-height: 1.3;
+}
+
+.portfolio-section > h2 {
+  margin-block: var(--space-1) var(--space-2);
+  font-size: var(--step-2);
+}
+
+.portfolio-section > p:not(.route-label),
+.portfolio-section article > p,
+.portfolio-section dd {
+  color: var(--text-muted);
+}
+
+.portfolio-section > * + *,
+.portfolio-section article > * + *,
+.portfolio-section li + li {
+  margin-block-start: var(--space-2);
+}
+
+.portfolio-section article {
+  min-width: 0;
+  margin-block-start: var(--space-3);
+  padding-block-start: var(--space-3);
+  border-block-start: 1px solid var(--line);
+}
+
+.portfolio-section article h3,
+.portfolio-section section h3 {
+  font-size: var(--step-1);
+}
+
+.portfolio-section ul,
+.portfolio-section ol {
+  padding-inline-start: 1.2rem;
+}
+
+.portfolio-section dl {
+  display: grid;
+  gap: var(--space-1) var(--space-2);
+  margin-block-start: var(--space-3);
+}
+
+.portfolio-section dt {
+  color: var(--cyan);
+  font-family: var(--mono);
+  font-size: var(--step--1);
+  font-weight: 650;
+  letter-spacing: 0.04em;
+}
+
+.portfolio-section dd {
+  min-width: 0;
+  margin-inline-start: 0;
+}
+
+.portfolio-section figure {
+  min-width: 0;
+  margin-block-start: var(--space-3);
+  padding: var(--space-2);
+  border: 1px solid var(--line);
+  background: var(--surface-raised);
+}
+
+.portfolio-section figcaption {
+  margin-block-start: var(--space-1);
+  color: var(--text-muted);
+  font-size: var(--step--1);
+}
+
+.portfolio-section svg {
+  inline-size: 100%;
+  block-size: auto;
+}
+
+.portfolio-section svg rect {
+  fill: #172432;
+  stroke: var(--cyan);
+  stroke-width: 2;
+}
+
+.portfolio-section svg text {
+  fill: var(--text);
+  font-family: var(--sans);
+  font-size: 19px;
+}
+
+.portfolio-section > div {
+  display: grid;
+  gap: var(--space-3);
+  margin-block-start: var(--space-3);
+}
+
+.portfolio-section > div > section {
+  min-width: 0;
+  padding-block-start: var(--space-2);
+  border-block-start: 1px solid var(--line);
+}
+
+.portfolio-section > div > section ul {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--space-1);
+  margin-block-start: var(--space-2);
+  padding: 0;
+  list-style: none;
+}
+
+.portfolio-section > div > section li {
+  display: inline-flex;
+  gap: 0.45rem;
+  align-items: center;
+  min-block-size: 2rem;
+  padding: 0.25rem 0.55rem;
+  border: 1px solid var(--line);
+  color: var(--text-muted);
+  font-size: var(--step--1);
+}
+
+.portfolio-section > div > section li span[aria-hidden='true'] {
+  inline-size: 0.5rem;
+  block-size: 0.5rem;
+  border: 1px solid var(--cyan);
+  border-radius: 50%;
+}
diff --git a/src/styles/layout.css b/src/styles/layout.css
new file mode 100644
index 0000000..f9e19da
--- /dev/null
+++ b/src/styles/layout.css
@@ -0,0 +1,127 @@
+.portfolio-shell {
+  min-width: 0;
+}
+
+.site-header {
+  display: grid;
+  gap: var(--space-2);
+  min-width: 0;
+  padding: var(--space-4) 4vw var(--space-3);
+  border-block-end: var(--panel-border);
+  background: #0b111b;
+}
+
+.site-header h1 {
+  font-size: var(--step-3);
+}
+
+.site-header > p:not(.route-label) {
+  color: var(--text-muted);
+  font-size: var(--step-1);
+}
+
+.site-navigation {
+  margin-block-start: var(--space-1);
+}
+
+.site-navigation ul {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.25rem;
+  max-inline-size: 78rem;
+  margin: 0;
+  padding: 0;
+  list-style: none;
+}
+
+.site-navigation a {
+  display: inline-flex;
+  align-items: center;
+  min-block-size: 44px;
+  padding-inline: 0.7rem;
+  color: var(--text-muted);
+  font-family: var(--mono);
+  font-size: var(--step--1);
+  letter-spacing: 0.04em;
+  text-decoration: none;
+  transition: color var(--transition), background-color var(--transition);
+}
+
+.site-navigation a:hover,
+.site-navigation a:focus-visible {
+  background: var(--cyan-deep);
+  color: var(--text);
+}
+
+.portfolio-main {
+  min-width: 0;
+  padding-block: var(--space-4) var(--space-5);
+}
+
+.portfolio-section {
+  width: calc(100% - 2rem);
+  min-width: 0;
+  margin: 0 1rem var(--space-4);
+  padding: var(--space-3);
+  scroll-margin-block: var(--space-3);
+  border: var(--panel-border);
+  border-radius: 2px;
+  background: var(--surface);
+  box-shadow: var(--panel-shadow);
+  transition: border-color var(--transition), background-color var(--transition);
+}
+
+.portfolio-section:hover {
+  border-color: var(--line-strong);
+}
+
+.site-footer,
+.portfolio-section footer {
+  display: grid;
+  gap: var(--space-2);
+  min-width: 0;
+}
+
+.site-footer {
+  padding: var(--space-4) 4vw;
+  border-block-start: var(--panel-border);
+  background: #0b111b;
+}
+
+@media (min-width: 768px) {
+  .site-header {
+    padding-inline: 5vw;
+  }
+
+  .portfolio-section {
+    width: calc(50% - 3rem);
+    margin-inline: 2rem 0;
+  }
+
+  .portfolio-section:nth-child(even) {
+    margin-inline-start: calc(50% + 1rem);
+  }
+
+  .site-footer {
+    padding-inline: 5vw;
+  }
+}
+
+@media (min-width: 1280px) {
+  .site-header {
+    padding-inline: 4vw;
+  }
+
+  .portfolio-section {
+    width: 42%;
+    margin-inline: 4% 0;
+  }
+
+  .portfolio-section:nth-child(even) {
+    margin-inline-start: 54%;
+  }
+
+  .site-footer {
+    padding-inline: 4vw;
+  }
+}
diff --git a/src/styles/print.css b/src/styles/print.css
new file mode 100644
index 0000000..fb5b8fa
--- /dev/null
+++ b/src/styles/print.css
@@ -0,0 +1,61 @@
+@media print {
+  :root {
+    color-scheme: light;
+    --text: #121820;
+    --text-muted: #374151;
+    --cyan: #0e5c72;
+    --surface: #fff;
+    --line: #8b98a5;
+  }
+
+  html,
+  body {
+    background: #fff;
+    color: var(--text);
+  }
+
+  .skip-link,
+  .site-navigation,
+  [data-decorative-world],
+  [data-scene-control] {
+    display: none !important;
+  }
+
+  .portfolio-shell,
+  .site-header,
+  .portfolio-main,
+  .site-footer {
+    display: block;
+    padding: 0;
+    border: 0;
+    background: transparent;
+  }
+
+  .site-header {
+    margin-block-end: 1.5rem;
+  }
+
+  .portfolio-section {
+    width: 100%;
+    margin: 0 0 1.25rem;
+    padding: 0 0 1.25rem;
+    break-inside: avoid;
+    border: 0;
+    border-block-end: 1px solid var(--line);
+    border-radius: 0;
+    background: transparent;
+    box-shadow: none;
+  }
+
+  a {
+    color: inherit;
+    text-decoration: underline;
+  }
+
+  a[href^='http']::after,
+  a[href^='mailto:']::after {
+    content: ' (' attr(href) ')';
+    font-size: 0.85em;
+    overflow-wrap: anywhere;
+  }
+}
diff --git a/src/styles/tokens.css b/src/styles/tokens.css
new file mode 100644
index 0000000..82aeef1
--- /dev/null
+++ b/src/styles/tokens.css
@@ -0,0 +1,29 @@
+:root {
+  color-scheme: dark;
+  --canvas: #080d16;
+  --surface: #101722;
+  --surface-raised: #141e2b;
+  --line: #314154;
+  --line-strong: #4a6275;
+  --text: #f2f4f5;
+  --text-muted: #b5c0c9;
+  --cyan: #80d9e6;
+  --cyan-deep: #163b48;
+  --amber: #f5b752;
+  --focus: #ffd17a;
+  --sans: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
+  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
+  --step--1: clamp(0.82rem, 0.78rem + 0.14vw, 0.92rem);
+  --step-0: clamp(1rem, 0.94rem + 0.24vw, 1.15rem);
+  --step-1: clamp(1.3rem, 1.14rem + 0.68vw, 1.75rem);
+  --step-2: clamp(1.9rem, 1.5rem + 1.35vw, 2.85rem);
+  --step-3: clamp(2.45rem, 1.82rem + 2.25vw, 4rem);
+  --space-1: clamp(0.5rem, 0.45rem + 0.2vw, 0.68rem);
+  --space-2: clamp(0.85rem, 0.75rem + 0.38vw, 1.15rem);
+  --space-3: clamp(1.3rem, 1.1rem + 0.7vw, 1.9rem);
+  --space-4: clamp(2rem, 1.65rem + 1.1vw, 3rem);
+  --space-5: clamp(3.25rem, 2.5rem + 2.6vw, 6rem);
+  --panel-border: 1px solid var(--line);
+  --panel-shadow: 0 14px 34px rgb(0 0 0 / 18%);
+  --transition: 160ms ease;
+}
diff --git a/tests/browser/responsive-layout.spec.ts b/tests/browser/responsive-layout.spec.ts
new file mode 100644
index 0000000..0fd9fab
--- /dev/null
+++ b/tests/browser/responsive-layout.spec.ts
@@ -0,0 +1,154 @@
+import { existsSync, readFileSync } from 'node:fs';
+import { resolve } from 'node:path';
+import { expect, test, type Page, type TestInfo } from '@playwright/test';
+
+const stylesheetFiles = [
+  'src/styles/tokens.css',
+  'src/styles/base.css',
+  'src/styles/layout.css',
+  'src/styles/components.css',
+  'src/styles/print.css',
+];
+
+function informationLayerCss(): string {
+  return stylesheetFiles
+    .map((file) => {
+      const path = resolve(process.cwd(), file);
+      return existsSync(path) ? readFileSync(path, 'utf8') : '';
+    })
+    .join('\n');
+}
+
+function informationLayerHarness(): string {
+  const navigation = ['Start', 'Profile', 'Experience', 'Infrastructure', 'Selected builds', 'Contact'];
+  const sections = ['start', 'profile', 'experience', 'infrastructure', 'selected-builds', 'contact'];
+
+  return `<!doctype html>
+    <html lang="en">
+    <head>
+      <meta name="viewport" content="width=device-width, initial-scale=1">
+      <style>${informationLayerCss()}</style>
+    </head>
+    <body>
+    <a class="skip-link" href="#portfolio-content">Skip to portfolio content</a>
+    <div class="portfolio-shell">
+      <header class="site-header">
+        <p class="route-label">00 / INTRODUCTION</p>
+        <h1>Luca Pîslaru</h1>
+        <p class="role">System Administrator &amp; Full-Stack Developer</p>
+        <nav class="site-navigation" aria-label="Portfolio sections">
+          <ul>${navigation.map((label, index) => `<li><a href="#${sections[index] ?? 'contact'}">${label}</a></li>`).join('')}</ul>
+        </nav>
+      </header>
+      <main id="portfolio-content" class="portfolio-main">
+        ${sections.map((id, index) => `
+          <section id="${id}" class="portfolio-section" data-section-index="${index + 1}" aria-labelledby="${id}-heading">
+            <p class="route-label">${String(index + 1).padStart(2, '0')} / ${id.toUpperCase()}</p>
+            <h2 id="${id}-heading">${navigation[index] ?? 'Contact'}</h2>
+            <p>Reliable systems and software evidence for hiring managers and technical interviewers.</p>
+            <article>
+              <h3>Operational detail</h3>
+              <p>Long unbroken technical reference: serviceorchestrationandobservabilityintegrationwithaverylongidentifierexampletestarchitectureproductionreadiness.</p>
+              <a href="https://example.test/portfolio/reference">Open project reference</a>
+            </article>
+          </section>
+        `).join('')}
+      </main>
+      <footer class="site-footer"><a href="mailto:luca@example.test">luca@example.test</a></footer>
+    </div>
+    </body>
+    </html>`;
+}
+
+async function loadInformationLayer(page: Page): Promise<void> {
+  await page.setContent(informationLayerHarness());
+}
+
+async function capture(page: Page, testInfo: TestInfo, name: string): Promise<void> {
+  await page.screenshot({ path: testInfo.outputPath(name), fullPage: true });
+}
+
+for (const viewport of [
+  { width: 320, height: 800 },
+  { width: 768, height: 1024 },
+  { width: 1440, height: 900 },
+  { width: 2560, height: 1440 },
+]) {
+  test(`keeps information content within the viewport at ${viewport.width}px`, async ({ page }, testInfo) => {
+    await page.setViewportSize(viewport);
+    await loadInformationLayer(page);
+
+    const geometry = await page.evaluate(() => {
+      const root = document.documentElement;
+      const boxes = [...document.querySelectorAll<HTMLElement>('.portfolio-shell :is(h1, h2, h3, p, a, article, section)')]
+        .map((element) => element.getBoundingClientRect())
+        .filter((rect) => rect.width > 0 && rect.height > 0);
+      return {
+        noOverflow: root.scrollWidth <= root.clientWidth + 1,
+        allBoxesFit: boxes.every((rect) => rect.left >= -1 && rect.right <= root.clientWidth + 1),
+      };
+    });
+
+    await capture(page, testInfo, `information-layer-${viewport.width}.png`);
+    expect(geometry.noOverflow).toBe(true);
+    expect(geometry.allBoxesFit).toBe(true);
+  });
+}
+
+test('uses alternating desktop panels while preserving a clear central road corridor', async ({ page }, testInfo) => {
+  await page.setViewportSize({ width: 1440, height: 900 });
+  await loadInformationLayer(page);
+
+  const panels = await page.locator('.portfolio-main > .portfolio-section').evaluateAll((sections, viewportWidth) =>
+    sections.map((section) => {
+      const rect = section.getBoundingClientRect();
+      return { left: rect.left, right: rect.right, widthRatio: rect.width / Number(viewportWidth) };
+    }), 1440,
+  );
+
+  expect(panels.every((panel) => panel.widthRatio >= 0.4 && panel.widthRatio <= 0.45)).toBe(true);
+  expect(panels.every((panel, index) => index % 2 === 0 ? panel.right <= 1440 * 0.461 : panel.left >= 1440 * 0.539)).toBe(true);
+  await capture(page, testInfo, 'information-layer-desktop-corridor.png');
+});
+
+test('uses a stable tablet rhythm and a single readable mobile column with usable navigation targets', async ({ page }, testInfo) => {
+  await page.setViewportSize({ width: 768, height: 1024 });
+  await loadInformationLayer(page);
+  const tabletPanels = await page.locator('.portfolio-main > .portfolio-section').evaluateAll((sections) =>
+    sections.map((section) => section.getBoundingClientRect()),
+  );
+  expect(tabletPanels.every((panel) => panel.width < 768 * 0.7)).toBe(true);
+  expect(tabletPanels.every((panel, index) => index % 2 === 0 ? panel.left < 768 / 2 : panel.left >= 768 / 2)).toBe(true);
+  await capture(page, testInfo, 'information-layer-tablet.png');
+
+  await page.setViewportSize({ width: 320, height: 800 });
+  await loadInformationLayer(page);
+  const mobile = await page.evaluate(() => {
+    const root = document.documentElement;
+    const panels = [...document.querySelectorAll<HTMLElement>('.portfolio-main > .portfolio-section')]
+      .map((section) => section.getBoundingClientRect());
+    const navigationTargets = [...document.querySelectorAll<HTMLElement>('.site-navigation a')]
+      .map((link) => link.getBoundingClientRect());
+    return {
+      singleColumn: panels.every((panel) => panel.left >= 0 && panel.right <= root.clientWidth && panel.width >= root.clientWidth * 0.85),
+      touchTargets: navigationTargets.every((target) => target.width >= 44 && target.height >= 44),
+    };
+  });
+  expect(mobile.singleColumn).toBe(true);
+  expect(mobile.touchTargets).toBe(true);
+  await capture(page, testInfo, 'information-layer-mobile.png');
+});
+
+test('removes nonessential information-layer motion when reduced motion is requested', async ({ page }) => {
+  await page.emulateMedia({ reducedMotion: 'reduce' });
+  await loadInformationLayer(page);
+  const duration = await page.locator('.portfolio-section').first().evaluate((element) => getComputedStyle(element).transitionDuration);
+  expect(duration).toBe('0.001s');
+});
+
+test('creates a clean print portfolio with navigation removed', async ({ page }) => {
+  await page.emulateMedia({ media: 'print' });
+  await loadInformationLayer(page);
+  await expect(page.locator('.site-navigation')).toBeHidden();
+  await expect(page.locator('.portfolio-section').first()).toHaveCSS('break-inside', 'avoid');
+});
diff --git a/vitest.config.ts b/vitest.config.ts
index 5ef219c..2227058 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -10,6 +10,7 @@ export default defineConfig({
   test: {
     environment: 'happy-dom',
     globals: false,
+    include: ['tests/unit/**/*.test.ts', 'tests/integration/**/*.test.{ts,mjs}'],
     coverage: { include: ['src/**/*.{ts,vue}'] },
   },
 });