/* ═══════════════════════════════════════════════════════════
   Biomimetics.dev - Design System v2
   Dark theme · Nature-inspired emerald accent · Professional
   ═══════════════════════════════════════════════════════════ */

/* ── Custom Properties ────────────────────────────────────── */
:root {
  /* Backgrounds - deep dark navy */
  --bg-primary:    #0f1117;
  --bg-secondary:  #0b0e15;
  --bg-card:       #161c28;
  --bg-card-hover: #1c2336;
  --bg-elevated:   #1a2030;

  /* Text */
  --text-primary:   #eef2ff;
  --text-secondary: #7b90b8;
  --text-muted:     #7287ac;

  /* Accent - Emerald green (nature-inspired) */
  --accent:       #4ade80;
  --accent-hover: #86efac;
  --accent-dim:   rgba(74, 222, 128, 0.10);
  --accent-glow:  rgba(74, 222, 128, 0.15);
  --accent-border: rgba(74, 222, 128, 0.28);
  --accent-subtle: rgba(74, 222, 128, 0.18);

  /* In-text links (distinct from accent for readability) */
  --link:       #60a5fa;
  --link-hover: #93c5fd;

  /* Borders */
  --border:       rgba(255, 255, 255, 0.07);
  --border-light: rgba(255, 255, 255, 0.13);

  /* Feedback */
  --success: #4ade80;
  --warning: #fbbf24;

  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  --font-mono: 'Cascadia Code', 'Fira Code', 'JetBrains Mono', Consolas, monospace;

  /* Type scale */
  --text-xs:   0.75rem;
  --text-sm:   0.875rem;
  --text-base: 1rem;
  --text-lg:   1.125rem;
  --text-xl:   1.25rem;
  --text-2xl:  1.5rem;
  --text-3xl:  1.875rem;
  --text-4xl:  2.5rem;
  --text-5xl:  3.5rem;

  /* Spacing */
  --space-1:  0.25rem;
  --space-2:  0.5rem;
  --space-3:  0.75rem;
  --space-4:  1rem;
  --space-5:  1.25rem;
  --space-6:  1.5rem;
  --space-8:  2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;

  /* Layout */
  --header-height: 64px;
  --max-width:     1100px;
  --article-width: 760px;

  /* Border radii */
  --radius:    0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1.25rem;

  /* Shadows */
  --shadow-sm: 0 1px 4px rgba(0, 0, 0, 0.5);
  --shadow:    0 4px 16px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.6);

  /* Transitions */
  --ease:     180ms ease;
  --ease-out: 280ms cubic-bezier(0.16, 1, 0.3, 1);
}

/* ── Reset ────────────────────────────────────────────────── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  background-color: var(--bg-primary);
}

body {
  font-family: var(--font-sans);
  background: transparent;
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ── Animated background canvas ──────────────────────────── */
#bg-canvas {
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  width: 100%;
  height: 100%;
  max-width: none;
  display: block;
}

img, video, canvas {
  max-width: 100%;
  display: block;
}

a {
  color: var(--link);
  text-decoration: none;
  transition: color var(--ease);
}

a:hover {
  color: var(--link-hover);
  text-decoration: underline;
}

/* ── Sticky Header ────────────────────────────────────────── */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-height);
  background: rgba(15, 17, 23, 0.88);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}

.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-6);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-6);
}

.logo {
  display: inline-flex;
  align-items: center;
  gap: var(--space-3);
  background: none;
  border: none;
  font-family: var(--font-sans);
  font-size: var(--text-lg);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--text-primary);
  cursor: pointer;
  padding: 0;
  text-decoration: none;
  flex-shrink: 0;
  transition: opacity var(--ease);
}

.logo:hover {
  opacity: 0.82;
  text-decoration: none;
  color: var(--text-primary);
}

.logo-hex {
  width: 26px;
  height: 26px;
  color: var(--accent);
  flex-shrink: 0;
}

.main-nav {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}

.nav-link {
  background: none;
  border: none;
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--text-secondary);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius);
  cursor: pointer;
  transition: color var(--ease), background var(--ease);
  white-space: nowrap;
}

.nav-link:hover {
  color: var(--text-primary);
  background: rgba(255, 255, 255, 0.05);
}

.nav-link.active {
  color: var(--accent);
  background: var(--accent-dim);
}

.hamburger {
  display: none;
  align-items: center;
  justify-content: center;
  background: none;
  border: none;
  color: var(--text-secondary);
  cursor: pointer;
  padding: var(--space-2);
  border-radius: var(--radius);
  transition: color var(--ease);
  flex-shrink: 0;
}

.hamburger:hover {
  color: var(--text-primary);
}

/* ── Main content area ────────────────────────────────────── */
#content-area {
  flex: 1;
  max-width: var(--max-width);
  margin: 0 auto;
  width: 100%;
  padding: 0 var(--space-6);
  position: relative;
  z-index: 1;
}

/* Fade-up animation when content loads */
@keyframes fadeUp {
  from { opacity: 0; transform: translateY(10px); }
  to   { opacity: 1; transform: translateY(0); }
}

#content > * {
  animation: fadeUp 250ms ease-out both;
}

/* ── Hero section (homepage) ─────────────────────────────── */
.home {
  padding-bottom: var(--space-16);
}

.hero {
  position: relative;
  padding: var(--space-20) 0 var(--space-16);
  text-align: center;
  overflow: hidden;
}

/* Pulsing radial glow behind the headline */
.hero::before {
  content: '';
  position: absolute;
  top: 45%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 800px;
  height: 600px;
  background: radial-gradient(ellipse at center,
    rgba(74, 222, 128, 0.07) 0%,
    transparent 65%);
  pointer-events: none;
  animation: glowPulse 5s ease-in-out infinite;
}

@keyframes glowPulse {
  0%, 100% { opacity: 0.7; }
  50%       { opacity: 1.0; }
}

.hero-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  background: var(--accent-dim);
  border: 1px solid rgba(74, 222, 128, 0.22);
  padding: var(--space-1) var(--space-4);
  border-radius: 100px;
  margin-bottom: var(--space-6);
}

.hero-title {
  font-size: clamp(2.5rem, 8vw, 5rem);
  font-weight: 800;
  letter-spacing: -0.04em;
  line-height: 1.05;
  background: linear-gradient(135deg, #ffffff 35%, var(--accent) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: var(--space-5);
}

.hero-subtitle {
  font-size: clamp(1rem, 2.5vw, var(--text-xl));
  color: var(--text-secondary);
  max-width: 580px;
  margin: 0 auto var(--space-10);
  line-height: 1.7;
}

.hero-cta {
  display: flex;
  gap: var(--space-4);
  justify-content: center;
  flex-wrap: wrap;
}

/* ── Feature cards (homepage) ─────────────────────────────── */
.features {
  padding: var(--space-4) 0 var(--space-8);
}

.features-heading {
  text-align: center;
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-8);
}

.features-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-5);
}

.feature-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  cursor: pointer;
  transition: border-color var(--ease), background var(--ease),
              transform var(--ease-out), box-shadow var(--ease-out);
  text-align: left;
}

.feature-card:hover {
  border-color: var(--accent-border);
  background: var(--bg-card-hover);
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.feature-icon {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--accent-dim);
  border-radius: var(--radius);
  margin-bottom: var(--space-5);
  color: var(--accent);
  flex-shrink: 0;
}

.feature-card h3 {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-3);
  letter-spacing: -0.01em;
}

.feature-card p {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: 1.65;
  margin: 0;
}

.feature-arrow {
  display: inline-block;
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--accent);
  margin-top: var(--space-5);
  opacity: 0;
  transform: translateX(-6px);
  transition: opacity var(--ease), transform var(--ease);
}

.feature-card:hover .feature-arrow {
  opacity: 1;
  transform: translateX(0);
}

/* ── Feature card + blog entry as anchor links ───────────── */
a.feature-card,
a.blog-entry {
  text-decoration: none;
  color: inherit;
  display: block;
}

a.feature-card:hover,
a.blog-entry:hover {
  text-decoration: none;
  color: inherit;
}

/* ── Simulation card icon ─────────────────────────────────── */
.card-icon {
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--accent-dim);
  border-radius: var(--radius);
  margin-bottom: var(--space-5);
  color: var(--accent);
}

/* ── Blog meta row ────────────────────────────────────────── */
.blog-meta {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-bottom: var(--space-3);
}

.blog-date {
  font-size: var(--text-xs);
  color: var(--text-muted);
  font-weight: 500;
  letter-spacing: 0.03em;
}

.read-more {
  display: inline-block;
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--accent);
  margin-top: var(--space-4);
  transition: color var(--ease);
}

a.blog-entry:hover .read-more {
  color: var(--accent-hover);
}

/* ── Buttons ──────────────────────────────────────────────── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 600;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all var(--ease);
  text-decoration: none;
  white-space: nowrap;
  padding: var(--space-2) var(--space-4);
  border: 1px solid var(--border-light);
  background: transparent;
  color: var(--text-primary);
}

.btn:hover {
  background: rgba(255, 255, 255, 0.06);
  text-decoration: none;
  color: var(--text-primary);
}

.btn-primary {
  background: var(--accent);
  color: #052010;
  border-color: var(--accent);
  padding: var(--space-3) var(--space-6);
}

.btn-primary:hover {
  background: var(--accent-hover);
  border-color: var(--accent-hover);
  color: #052010;
  transform: translateY(-1px);
  box-shadow: 0 4px 20px var(--accent-glow);
  text-decoration: none;
}

.btn-outline {
  background: transparent;
  color: var(--text-primary);
  border: 1px solid var(--border-light);
  padding: var(--space-3) var(--space-6);
}

.btn-outline:hover {
  background: rgba(255, 255, 255, 0.06);
  border-color: rgba(255, 255, 255, 0.22);
  color: var(--text-primary);
  text-decoration: none;
}

/* Legacy accent button used by simulation page */
.btn-accent {
  background: var(--accent);
  color: #052010;
  border-color: var(--accent);
}

.btn-accent:hover {
  background: var(--accent-hover);
  border-color: var(--accent-hover);
}

/* ── Simulation cards ─────────────────────────────────────── */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--space-6);
}

.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  cursor: pointer;
  transition: background var(--ease), border-color var(--ease),
              transform var(--ease-out), box-shadow var(--ease-out);
}

.card:hover {
  background: var(--bg-card-hover);
  border-color: var(--accent-border);
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.card h3 {
  font-size: var(--text-xl);
  font-weight: 600;
  letter-spacing: -0.01em;
  margin-bottom: var(--space-3);
}

.card p {
  color: var(--text-secondary);
  font-size: var(--text-sm);
  line-height: 1.65;
}

.card .tag {
  display: inline-block;
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.04em;
  color: var(--accent);
  background: var(--accent-dim);
  border: 1px solid rgba(74, 222, 128, 0.2);
  padding: 2px var(--space-3);
  border-radius: 100px;
  margin-top: var(--space-4);
}

/* ── Article / Prose ──────────────────────────────────────── */
.article {
  max-width: var(--article-width);
  margin: 0 auto;
  padding: var(--space-10) 0 var(--space-16);
}

.article > h2 {
  font-size: clamp(1.75rem, 5vw, var(--text-4xl));
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.15;
  color: var(--text-primary);
  margin-bottom: var(--space-8);
}

.article h3 {
  font-size: var(--text-xl);
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--text-primary);
  margin-top: var(--space-10);
  margin-bottom: var(--space-4);
  padding-left: var(--space-4);
  border-left: 3px solid var(--accent);
}

.article p {
  color: var(--text-secondary);
  line-height: 1.8;
  margin-bottom: var(--space-5);
  font-size: var(--text-base);
}

.article strong {
  color: var(--text-primary);
  font-weight: 600;
}

.article ul, .article ol {
  margin-bottom: var(--space-5);
  padding-left: var(--space-6);
  color: var(--text-secondary);
}

.article li {
  margin-bottom: var(--space-2);
  line-height: 1.7;
}

.article img {
  border-radius: var(--radius-lg);
  margin: var(--space-8) 0;
}

.article blockquote {
  border-left: 3px solid var(--accent);
  padding: var(--space-4) var(--space-6);
  margin: var(--space-8) 0;
  background: var(--bg-card);
  border-radius: 0 var(--radius) var(--radius) 0;
  color: var(--text-secondary);
  font-style: italic;
}

/* Page intro subtitle under h2 */
.page-intro {
  margin-top: calc(-1 * var(--space-4));
  margin-bottom: var(--space-8);
}

.page-intro p {
  font-size: var(--text-lg);
  color: var(--text-secondary);
  max-width: 600px;
  line-height: 1.7;
}

/* ── What-is info section ─────────────────────────────────── */
.info-section {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  margin-top: var(--space-2);
}

.info-section p {
  color: var(--text-secondary);
  line-height: 1.8;
  margin-bottom: var(--space-5);
}

.info-section p:last-child {
  margin-bottom: 0;
}

/* ── Citations ────────────────────────────────────────────── */
.citation {
  color: var(--accent);
  font-size: 0.7em;
  vertical-align: super;
  font-weight: 700;
  cursor: pointer;
  text-decoration: none;
  transition: color var(--ease);
}

.citation:hover {
  color: var(--accent-hover);
  text-decoration: none;
}

/* ── References ───────────────────────────────────────────── */
.references {
  margin-top: var(--space-12);
  padding-top: var(--space-6);
  border-top: 1px solid var(--border);
}

.article .references h3,
.references h3 {
  font-size: var(--text-xs);
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-5);
  border-left: none;
  padding-left: 0;
  margin-top: 0;
}

.references ol {
  padding-left: var(--space-6);
  counter-reset: ref;
  list-style: none;
}

.references li {
  counter-increment: ref;
  margin-bottom: var(--space-4);
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: 1.65;
  padding-left: var(--space-2);
}

.references li::before {
  content: '[' counter(ref) ']';
  color: var(--accent);
  font-weight: 700;
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  margin-right: var(--space-3);
}

.references a {
  color: var(--link);
  word-break: break-all;
  font-size: var(--text-xs);
  font-family: var(--font-mono);
}

.references a:hover {
  color: var(--link-hover);
}

/* ── Simulation wrapper ───────────────────────────────────── */
.simulation-wrapper {
  position: relative;
  width: 100%;
  border-radius: var(--radius-xl);
  overflow: hidden;
  background: #0b0e15;
  border: 1px solid var(--border);
  box-shadow: var(--shadow-lg);
}

.simulation-wrapper canvas {
  display: block;
  width: 100%;
}

.simulation-controls {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-6);
  padding: var(--space-5) var(--space-6);
  background: var(--bg-card);
  border-top: 1px solid var(--border);
}

.control-group {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  min-width: 160px;
}

.control-group label {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.control-group input[type="range"] {
  accent-color: var(--accent);
  width: 100%;
  cursor: pointer;
}

.control-group input[type="range"]:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.control-group .value-display {
  font-size: var(--text-sm);
  color: var(--accent);
  font-family: var(--font-mono);
  font-weight: 600;
}

/* ── Back link ────────────────────────────────────────────── */
.back-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--text-muted);
  margin-bottom: var(--space-8);
  cursor: pointer;
  transition: color var(--ease), gap var(--ease-out);
  text-decoration: none;
  border: none;
  background: none;
  font-family: var(--font-sans);
  padding: 0;
}

.back-link:hover {
  color: var(--accent);
  gap: var(--space-3);
  text-decoration: none;
}

/* ── Blog listing ─────────────────────────────────────────── */
.blog-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.blog-entry {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  padding: var(--space-6) var(--space-8);
  cursor: pointer;
  transition: background var(--ease), border-color var(--ease), transform var(--ease-out);
}

.blog-entry:hover {
  background: var(--bg-card-hover);
  border-color: rgba(74, 222, 128, 0.22);
  transform: translateX(4px);
}

.blog-entry h3 {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-2);
  letter-spacing: -0.01em;
}

.blog-entry .meta {
  font-size: var(--text-xs);
  color: var(--text-muted);
  font-weight: 500;
  letter-spacing: 0.03em;
  margin-bottom: var(--space-3);
}

.blog-entry p {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  line-height: 1.65;
  margin: 0;
}

.blog-entry-arrow {
  color: var(--text-muted);
  font-size: var(--text-xl);
  line-height: 1;
  flex-shrink: 0;
  transition: color var(--ease), transform var(--ease);
}

.blog-entry:hover .blog-entry-arrow {
  color: var(--accent);
  transform: translateX(3px);
}

/* ── Footer ───────────────────────────────────────────────── */
.site-footer {
  padding: var(--space-10) var(--space-6);
  border-top: 1px solid var(--border);
  margin-top: auto;
  position: relative;
  z-index: 1;
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--space-4);
}

.footer-inner p {
  font-size: var(--text-sm);
  color: var(--text-muted);
}

.footer-inner a {
  color: var(--text-secondary);
  text-decoration: none;
  transition: color var(--ease);
}

.footer-inner a:hover {
  color: var(--accent);
  text-decoration: none;
}

.footer-tagline {
  font-style: italic;
}

/* ── Simulation hint box ──────────────────────────────────── */
.sim-hint {
  background: var(--bg-card);
  border: 1px solid rgba(74, 222, 128, 0.22);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: var(--space-4) var(--space-6);
  margin-top: var(--space-5);
  color: var(--text-secondary);
  font-size: var(--text-sm);
  line-height: 1.7;
}

.sim-hint strong {
  color: var(--accent);
  font-weight: 700;
}

/* ── Math formula display block ──────────────────────────── */
.math-block {
  background: var(--bg-card);
  border: 1px solid var(--accent-subtle);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: var(--space-3) var(--space-8);
  margin: var(--space-6) auto;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 1.05rem;
  color: var(--text-primary);
  max-width: 520px;
  letter-spacing: 0.01em;
  line-height: 1.9;
}

/* ── Sim-viewport spacer (ensures observer has area to detect) */
.sim-viewport {
  margin: var(--space-8) 0;
}

/* ── Contact form ─────────────────────────────────────────── */
.contact-form {
  max-width: 560px;
  margin-top: var(--space-8);
}

.contact-honeypot {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  margin-bottom: var(--space-5);
}

.form-label {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--text-primary);
}

.form-required {
  color: var(--accent);
  margin-left: var(--space-1);
}

.form-input {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text-primary);
  font-family: var(--font-sans);
  font-size: var(--text-base);
  padding: var(--space-3) var(--space-4);
  transition: border-color var(--ease), box-shadow var(--ease);
  width: 100%;
  box-sizing: border-box;
}

.form-input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-dim);
}

.form-input::placeholder {
  color: var(--text-muted);
}

.form-textarea {
  resize: vertical;
  min-height: 140px;
  line-height: 1.6;
}

.form-status {
  font-size: var(--text-sm);
  min-height: 1.4rem;
  margin-bottom: var(--space-4);
  border-radius: var(--radius);
  padding: 0;
}

.form-status:not(:empty) {
  padding: var(--space-3) var(--space-4);
}

.form-status--error {
  color: #fca5a5;
  background: rgba(239, 68, 68, 0.12);
  border: 1px solid rgba(239, 68, 68, 0.25);
}

.form-status--success {
  color: var(--accent-hover);
  background: var(--accent-dim);
  border: 1px solid rgba(74, 222, 128, 0.25);
}

.form-submit {
  min-width: 10rem;
}

.form-submit:disabled {
  opacity: 0.6;
  cursor: not-allowed;
  transform: none;
}

/* ── Skip link (accessibility) ────────────────────────────── */
.skip-link {
  position: absolute;
  top: -100%;
  left: var(--space-4);
  z-index: 200;
  background: var(--accent);
  color: #052010;
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius);
  font-size: var(--text-sm);
  font-weight: 600;
  text-decoration: none;
  transition: top var(--ease);
}

.skip-link:focus {
  top: var(--space-2);
  color: #052010;
  text-decoration: none;
}

/* ── Screen-reader only (accessibility) ──────────────────── */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* ── Focus-visible styles (accessibility) ────────────────── */
:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

a.feature-card:focus-visible,
a.blog-entry:focus-visible,
.card:focus-visible {
  border-color: var(--accent-border);
}

/* ── Reader mode toggle ──────────────────────────────────── */
.reader-toggle {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text-secondary);
  font-family: var(--font-sans);
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.04em;
  padding: var(--space-1) var(--space-3);
  cursor: pointer;
  transition: color var(--ease), border-color var(--ease), background var(--ease);
  float: right;
  margin-top: var(--space-1);
}

.reader-toggle:hover {
  color: var(--accent);
  border-color: var(--accent-border);
  background: var(--bg-card-hover);
}

.reader-toggle svg {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
}

/* Reader mode active state */
body.reader-mode #bg-canvas,
body.reader-mode .site-header,
body.reader-mode .site-footer {
  display: none;
}

body.reader-mode {
  background: #fafafa;
  color: #1a1a1a;
}

body.reader-mode #content-area {
  max-width: var(--article-width);
  padding-top: var(--space-8);
}

body.reader-mode .article,
body.reader-mode article {
  padding-top: 0;
}

body.reader-mode .article > h2,
body.reader-mode article > h2 {
  color: #1a1a1a;
}

body.reader-mode .article h3,
body.reader-mode article h3 {
  color: #2a2a2a;
  border-left-color: #4ade80;
}

body.reader-mode .article p,
body.reader-mode article p,
body.reader-mode .article li,
body.reader-mode article li {
  color: #333;
}

body.reader-mode .article strong,
body.reader-mode article strong {
  color: #1a1a1a;
}

body.reader-mode .article blockquote,
body.reader-mode article blockquote {
  background: #f0f0f0;
  color: #444;
}

body.reader-mode .blog-meta .tag {
  background: rgba(74, 222, 128, 0.15);
  color: #16803c;
  border-color: rgba(74, 222, 128, 0.3);
}

body.reader-mode .blog-date {
  color: #666;
}

body.reader-mode .back-link {
  color: #666;
}

body.reader-mode .back-link:hover {
  color: #16803c;
}

body.reader-mode .references {
  border-top-color: #ddd;
}

body.reader-mode .references h3 {
  color: #888 !important;
}

body.reader-mode .math-block {
  background: #f0f0f0;
  border-color: rgba(22, 163, 74, 0.35);
  color: #1a1a1a;
}

body.reader-mode .references li {
  color: #555;
}

body.reader-mode .references a {
  color: #2563eb;
}

body.reader-mode .citation {
  color: #16803c;
}

body.reader-mode a {
  color: #2563eb;
}

body.reader-mode a:hover {
  color: #1d4ed8;
}

body.reader-mode .reader-toggle {
  background: #fff;
  border-color: #ccc;
  color: #555;
}

body.reader-mode .reader-toggle:hover {
  color: #16803c;
  border-color: #16803c;
}

/* Reader mode - dark colour scheme for users who prefer dark mode */
@media (prefers-color-scheme: dark) {
  body.reader-mode {
    background: #1a1a2e;
    color: #e0e0e0;
  }

  body.reader-mode .article > h2,
  body.reader-mode article > h2 {
    color: #f0f0f0;
  }

  body.reader-mode .article h3,
  body.reader-mode article h3 {
    color: #d4d4d4;
    border-left-color: #4ade80;
  }

  body.reader-mode .article p,
  body.reader-mode article p,
  body.reader-mode .article li,
  body.reader-mode article li {
    color: #c0c0c0;
  }

  body.reader-mode .article strong,
  body.reader-mode article strong {
    color: #f0f0f0;
  }

  body.reader-mode .article blockquote,
  body.reader-mode article blockquote {
    background: #252540;
    color: #b0b0b0;
  }

  body.reader-mode .blog-meta .tag {
    background: rgba(74, 222, 128, 0.12);
    color: #4ade80;
    border-color: rgba(74, 222, 128, 0.25);
  }

  body.reader-mode .blog-date {
    color: #888;
  }

  body.reader-mode .back-link {
    color: #888;
  }

  body.reader-mode .back-link:hover {
    color: #4ade80;
  }

  body.reader-mode .references {
    border-top-color: #333;
  }

  body.reader-mode .references h3 {
    color: #666 !important;
  }

  body.reader-mode .math-block {
    background: #252540;
    border-color: rgba(74, 222, 128, 0.22);
    color: #e0e0e0;
  }

  body.reader-mode .references li {
    color: #999;
  }

  body.reader-mode .references a {
    color: #60a5fa;
  }

  body.reader-mode .citation {
    color: #4ade80;
  }

  body.reader-mode a {
    color: #60a5fa;
  }

  body.reader-mode a:hover {
    color: #93c5fd;
  }

  body.reader-mode .reader-toggle {
    background: #252540;
    border-color: #444;
    color: #aaa;
  }

  body.reader-mode .reader-toggle:hover {
    color: #4ade80;
    border-color: #4ade80;
  }
}

/* ── Utility ─────────────────────────────────────────────── */
.text-center { text-align: center; }
.mt-4  { margin-top: var(--space-4); }
.mt-6  { margin-top: var(--space-6); }
.mt-8  { margin-top: var(--space-8); }
.mb-4  { margin-bottom: var(--space-4); }
.mb-8  { margin-bottom: var(--space-8); }

/* ── Responsive ──────────────────────────────────────────── */
@media (max-width: 768px) {
  /* Mobile nav drawer */
  .main-nav {
    display: none;
    position: absolute;
    top: var(--header-height);
    left: 0;
    right: 0;
    background: rgba(15, 17, 23, 0.97);
    backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--border);
    flex-direction: column;
    padding: var(--space-4) var(--space-6);
    gap: var(--space-1);
    align-items: stretch;
  }

  .main-nav.open {
    display: flex;
  }

  .nav-link {
    padding: var(--space-3) var(--space-4);
    font-size: var(--text-base);
  }

  .hamburger {
    display: flex;
  }

  .features-grid {
    grid-template-columns: 1fr;
    gap: var(--space-4);
  }

  .hero {
    padding: var(--space-16) 0 var(--space-10);
  }

  .hero-cta {
    flex-direction: column;
    align-items: center;
  }

  .card-grid {
    grid-template-columns: 1fr;
  }

  .blog-entry {
    grid-template-columns: 1fr;
  }

  .blog-entry-arrow {
    display: none;
  }

  .simulation-controls {
    flex-direction: column;
  }

  #content-area {
    padding: 0 var(--space-4);
  }

  .header-inner {
    padding: 0 var(--space-4);
  }
}

@media (max-width: 480px) {
  .article > h2 {
    font-size: var(--text-2xl);
  }

  .btn-primary,
  .btn-outline {
    width: 100%;
    justify-content: center;
    max-width: 280px;
  }

  .footer-inner {
    flex-direction: column;
    text-align: center;
  }
}

/* ── Reduced motion (accessibility) ──────────────────────── */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }

  #bg-canvas {
    display: none;
  }
}

/* ── High contrast (accessibility) ───────────────────────── */
@media (prefers-contrast: more) {
  :root {
    --border:       rgba(255, 255, 255, 0.25);
    --border-light: rgba(255, 255, 255, 0.35);
    --text-secondary: #a4b5d4;
    --text-muted:     #96a8c8;
  }

  a { text-decoration: underline; }
  a.feature-card,
  a.blog-entry,
  .nav-link { text-decoration: none; }

  .card,
  .feature-card,
  .blog-entry {
    border-width: 2px;
  }
}