/* =============================================================
   PORTFOLIO DESIGN SYSTEM
   HSL-based, dark-mode-first, single-font (Inter)
   ============================================================= */

/* =========================
   1. DESIGN TOKENS
   ========================= */
:root {
  /* Brand hue — blue-cyan range */
  --hue: 210;
  --sat: 60%;

  /* Timing */
  --transition-base: 0.3s ease;
  --transition-fast: 0.15s ease;

  /* Layout */
  --container-max: 1100px;
  --nav-height: 64px;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
}

/* ----- DARK MODE (default) ----- */
[data-theme="dark"] {
  /* Surfaces: 0% → 5% → 10% (lighter = closer to user) */
  --bg-base: hsl(var(--hue), 10%, 0%);
  --bg-card: hsl(var(--hue), 10%, 5%);
  --bg-raised: hsl(var(--hue), 10%, 10%);
  --bg-hover: hsl(var(--hue), 10%, 13%);

  /* Text hierarchy */
  --text-heading: hsl(0, 0%, 90%);
  --text-body: hsl(0, 0%, 72%);
  --text-muted: hsl(0, 0%, 50%);

  /* Primary accent */
  --primary: hsl(var(--hue), var(--sat), 55%);
  --primary-hover: hsl(var(--hue), var(--sat), 65%);
  --primary-subtle: hsl(var(--hue), var(--sat), 15%);

  /* Borders */
  --border-card: hsl(var(--hue), 10%, 12%);
  --border-card-hover: hsl(var(--hue), 10%, 20%);

  /* Card gradient: light from above */
  --card-gradient: linear-gradient(
    180deg,
    hsl(var(--hue), 10%, 7%) 0%,
    hsl(var(--hue), 10%, 4%) 100%
  );
  --card-gradient-hover: linear-gradient(
    180deg,
    hsl(var(--hue), 10%, 10%) 0%,
    hsl(var(--hue), 10%, 5%) 100%
  );

  /* Dark mode depth: lighter top border sells "raised" */
  --card-highlight: hsl(var(--hue), 10%, 15%);
  --card-shadow: none;
  --card-shadow-hover: none;

  /* Scrollbar */
  --scrollbar-track: hsl(var(--hue), 10%, 5%);
  --scrollbar-thumb: hsl(var(--hue), 10%, 18%);

  /* Nav */
  --nav-bg: hsla(var(--hue), 10%, 0%, 0.8);
}

/* ----- LIGHT MODE ----- */
[data-theme="light"] {
  /* Surfaces: inverted (100 - dark values) */
  --bg-base: hsl(var(--hue), 10%, 98%);
  --bg-card: hsl(var(--hue), 10%, 95%);
  --bg-raised: hsl(var(--hue), 10%, 90%);
  --bg-hover: hsl(var(--hue), 10%, 87%);

  /* Text hierarchy: inverted */
  --text-heading: hsl(0, 0%, 10%);
  --text-body: hsl(0, 0%, 28%);
  --text-muted: hsl(0, 0%, 50%);

  /* Primary — slightly darker for contrast on light bg */
  --primary: hsl(var(--hue), var(--sat), 45%);
  --primary-hover: hsl(var(--hue), var(--sat), 38%);
  --primary-subtle: hsl(var(--hue), var(--sat), 92%);

  /* Borders */
  --border-card: hsl(var(--hue), 10%, 88%);
  --border-card-hover: hsl(var(--hue), 10%, 78%);

  /* Card gradient */
  --card-gradient: linear-gradient(
    180deg,
    hsl(var(--hue), 10%, 97%) 0%,
    hsl(var(--hue), 10%, 93%) 100%
  );
  --card-gradient-hover: linear-gradient(
    180deg,
    hsl(var(--hue), 10%, 99%) 0%,
    hsl(var(--hue), 10%, 94%) 100%
  );

  /* Light mode depth: highlight + dual shadows */
  --card-highlight: hsl(var(--hue), 10%, 100%);
  --card-shadow:
    0 1px 3px hsla(var(--hue), 10%, 0%, 0.06),
    0 6px 16px hsla(var(--hue), 10%, 0%, 0.04);
  --card-shadow-hover:
    0 2px 6px hsla(var(--hue), 10%, 0%, 0.08),
    0 12px 28px hsla(var(--hue), 10%, 0%, 0.06);

  /* Scrollbar */
  --scrollbar-track: hsl(var(--hue), 10%, 95%);
  --scrollbar-thumb: hsl(var(--hue), 10%, 75%);

  /* Nav */
  --nav-bg: hsla(var(--hue), 10%, 98%, 0.85);
}

/* =========================
   2. RESET & BASE
   ========================= */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  font-weight: 400;
  line-height: 1.6;
  color: var(--text-body);
  background-color: var(--bg-base);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

/* Scrollbar */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--scrollbar-track); }
::-webkit-scrollbar-thumb {
  background: var(--scrollbar-thumb);
  border-radius: 3px;
}

/* =========================
   3. TYPOGRAPHY
   ========================= */
h1, h2, h3, h4 {
  font-family: 'Inter', sans-serif;
  color: var(--text-heading);
  line-height: 1.2;
}

h1 {
  font-size: 3.5rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}

h2 {
  font-size: 2rem;
  font-weight: 600;
  letter-spacing: -0.02em;
}

h3 {
  font-size: 1.25rem;
  font-weight: 600;
}

h4 {
  font-size: 1rem;
  font-weight: 500;
}

p {
  max-width: 60ch;
}

a {
  color: var(--primary);
  text-decoration: none;
  transition: color var(--transition-base);
}

a:hover {
  color: var(--primary-hover);
}

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

/* =========================
   4. LAYOUT
   ========================= */
.container {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 1.5rem;
}

section {
  padding: 6rem 0;
}

/* Skip to content (accessibility) */
.skip-to-content {
  position: absolute;
  top: -100%;
  left: 1rem;
  z-index: 200;
  padding: 0.5rem 1rem;
  background: var(--primary);
  color: #fff;
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 500;
}

.skip-to-content:focus {
  top: 0.5rem;
}

/* =========================
   5. NAVIGATION
   ========================= */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-card);
  transition: background var(--transition-base);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: var(--nav-height);
}

.nav-brand {
  font-weight: 600;
  font-size: 1.1rem;
  color: var(--text-heading);
  transition: color var(--transition-base);
}

.nav-brand:hover {
  color: var(--primary);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 2rem;
  list-style: none;
}

.nav-links a {
  color: var(--text-muted);
  font-size: 0.875rem;
  font-weight: 500;
  transition: color var(--transition-base);
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--text-heading);
}

.nav-right {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

/* Language Switcher */
.lang-switcher {
  display: flex;
  gap: 0.25rem;
}

.lang-btn {
  background: none;
  border: 1px solid transparent;
  color: var(--text-muted);
  padding: 0.3rem 0.6rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.75rem;
  font-family: 'Inter', sans-serif;
  font-weight: 500;
  transition: all var(--transition-base);
}

.lang-btn:hover {
  color: var(--text-heading);
}

.lang-btn.active {
  color: var(--primary);
  border-color: var(--primary-subtle);
  background: var(--primary-subtle);
}

/* Theme Toggle */
.theme-toggle {
  background: none;
  border: 1px solid var(--border-card);
  color: var(--text-muted);
  padding: 0.4rem 0.75rem;
  border-radius: var(--radius-md);
  cursor: pointer;
  font-size: 0.8rem;
  font-family: 'Inter', sans-serif;
  font-weight: 500;
  transition: all var(--transition-base);
  white-space: nowrap;
}

.theme-toggle:hover {
  border-color: var(--border-card-hover);
  color: var(--text-heading);
}

/* Mobile Hamburger */
.hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 0.5rem;
  background: none;
  border: none;
  cursor: pointer;
}

.hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--text-heading);
  transition: all var(--transition-base);
  border-radius: 1px;
}

.hamburger.active span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}

.hamburger.active span:nth-child(2) {
  opacity: 0;
}

.hamburger.active span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

/* Mobile Menu */
.mobile-menu {
  display: none;
  position: fixed;
  top: var(--nav-height);
  left: 0;
  right: 0;
  background: var(--bg-card);
  border-bottom: 1px solid var(--border-card);
  padding: 1.5rem;
  z-index: 99;
}

.mobile-menu.open {
  display: block;
}

.mobile-menu ul {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.mobile-menu a {
  color: var(--text-body);
  font-size: 1rem;
  font-weight: 500;
  display: block;
  padding: 0.5rem 0;
}

.mobile-menu a:hover {
  color: var(--text-heading);
}

/* =========================
   6. HERO SECTION
   ========================= */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding-top: var(--nav-height);
}

.hero-content {
  max-width: 700px;
}

.hero-label {
  display: inline-block;
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--primary);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 1.5rem;
}

.hero h1 {
  margin-bottom: 1.5rem;
}

.hero h1 .accent {
  color: var(--primary);
}

.hero-subtitle {
  font-size: 1.2rem;
  color: var(--text-body);
  margin-bottom: 2.5rem;
  max-width: 55ch;
  line-height: 1.7;
}

.hero-cta {
  display: flex;
  gap: 1rem;
  align-items: center;
  flex-wrap: wrap;
}

/* =========================
   7. BUTTONS
   ========================= */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  border-radius: var(--radius-md);
  font-family: 'Inter', sans-serif;
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-base);
  border: none;
  text-decoration: none;
}

.btn-primary {
  background: var(--primary);
  color: #fff;
}

.btn-primary:hover {
  background: var(--primary-hover);
  color: #fff;
}

.btn-ghost {
  background: transparent;
  color: var(--text-body);
  border: 1px solid var(--border-card);
}

.btn-ghost:hover {
  border-color: var(--border-card-hover);
  color: var(--text-heading);
  background: var(--bg-card);
}

/* =========================
   8. SECTION HEADERS
   ========================= */
.section-header {
  margin-bottom: 3rem;
}

.section-label {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--primary);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.75rem;
}

.section-header p {
  color: var(--text-muted);
  font-size: 0.95rem;
  margin-top: 0.75rem;
}

/* =========================
   9. PROJECT CARDS
   ========================= */
.projects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1.5rem;
}

.project-card {
  background: var(--card-gradient);
  border: 1px solid var(--border-card);
  border-top-color: var(--card-highlight);
  border-radius: var(--radius-lg);
  overflow: hidden;
  cursor: pointer;
  transition: all var(--transition-base);
  position: relative;
  box-shadow: var(--card-shadow);
}

.project-card:hover {
  background: var(--card-gradient-hover);
  border-color: var(--border-card-hover);
  transform: translateY(-2px);
  box-shadow: var(--card-shadow-hover);
}

.project-card-image {
  width: 100%;
  height: 200px;
  overflow: hidden;
  background: var(--bg-raised);
  display: flex;
  align-items: center;
  justify-content: center;
}

.project-card-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.4s ease;
}

.project-card:hover .project-card-image img {
  transform: scale(1.03);
}

.project-card-image-placeholder {
  color: var(--text-muted);
  font-size: 0.85rem;
}

.project-card-body {
  padding: 1.5rem;
}

.project-card-body h3 {
  margin-bottom: 0.5rem;
}

.project-card-outcome {
  color: var(--text-body);
  font-size: 0.9rem;
  margin-bottom: 1rem;
  line-height: 1.6;
}

.project-card-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
}

.tag {
  font-size: 0.7rem;
  font-weight: 500;
  padding: 0.25rem 0.6rem;
  border-radius: var(--radius-sm);
  background: var(--primary-subtle);
  color: var(--primary);
}

.project-card-cta {
  padding: 1rem 1.5rem;
  border-top: 1px solid var(--border-card);
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 0.85rem;
  font-weight: 500;
  color: var(--primary);
}

.project-card-cta .arrow {
  transition: transform var(--transition-base);
  display: inline-block;
}

.project-card:hover .project-card-cta .arrow {
  transform: translateX(4px);
}

/* =========================
   10. CASE STUDY EXPANSION
   ========================= */
.case-study {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.5s ease, opacity 0.3s ease;
  opacity: 0;
}

.case-study.open {
  max-height: 1200px;
  opacity: 1;
}

.case-study-inner {
  padding: 2rem 0;
}

.case-study-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
}

.case-study-section h4 {
  color: var(--primary);
  text-transform: uppercase;
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  margin-bottom: 0.75rem;
}

.case-study-section p {
  font-size: 0.9rem;
  line-height: 1.7;
}

.case-study-tech {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 1.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border-card);
}

.tech-badge {
  font-size: 0.75rem;
  font-weight: 500;
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-md);
  background: var(--bg-raised);
  color: var(--text-body);
  border: 1px solid var(--border-card);
}

.case-study-actions {
  display: flex;
  gap: 0.75rem;
  margin-top: 1.5rem;
}

/* =========================
   11. DIVIDER
   ========================= */
.divider {
  width: 100%;
  height: 1px;
  background: var(--border-card);
}

/* =========================
   12. ABOUT / CONTACT
   ========================= */
.about-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4rem;
  align-items: start;
}

.about-text h2 {
  margin-bottom: 1.5rem;
}

.about-text p {
  margin-bottom: 1rem;
  font-size: 0.95rem;
  line-height: 1.7;
}

.about-meta {
  color: var(--text-muted);
  font-size: 0.85rem;
  margin-top: 1.5rem;
}

.contact-card {
  background: var(--card-gradient);
  border: 1px solid var(--border-card);
  border-top-color: var(--card-highlight);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: var(--card-shadow);
}

.contact-card h3 {
  margin-bottom: 1.5rem;
}

.contact-link {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem 0;
  color: var(--text-body);
  font-size: 0.9rem;
  border-bottom: 1px solid var(--border-card);
  transition: color var(--transition-base);
  text-decoration: none;
}

.contact-link:last-child {
  border-bottom: none;
}

.contact-link:hover {
  color: var(--primary);
}

.contact-link-icon {
  width: 20px;
  text-align: center;
  color: var(--text-muted);
  flex-shrink: 0;
}

/* =========================
   13. FOOTER
   ========================= */
.footer {
  padding: 2rem 0;
  border-top: 1px solid var(--border-card);
  text-align: center;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.footer-inner {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
}

.footer-links {
  display: flex;
  gap: 1.5rem;
}

.footer-links a {
  color: var(--text-muted);
  transition: color var(--transition-base);
}

.footer-links a:hover {
  color: var(--text-heading);
}

/* =========================
   14. ANIMATIONS
   ========================= */
@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.fade-up {
  opacity: 0;
}

.fade-up.is-visible {
  animation: fadeUp 0.6s ease forwards;
}

.fade-up.is-visible.delay-1 { animation-delay: 0.1s; }
.fade-up.is-visible.delay-2 { animation-delay: 0.2s; }
.fade-up.is-visible.delay-3 { animation-delay: 0.3s; }
.fade-up.is-visible.delay-4 { animation-delay: 0.4s; }

/* =========================
   15. RESPONSIVE
   ========================= */
@media (max-width: 768px) {
  h1 {
    font-size: 2.25rem;
  }

  h2 {
    font-size: 1.5rem;
  }

  section {
    padding: 4rem 0;
  }

  /* Nav */
  .nav-links {
    display: none;
  }

  .hamburger {
    display: flex;
  }

  /* Hero */
  .hero {
    min-height: auto;
    padding-top: calc(var(--nav-height) + 3rem);
    padding-bottom: 3rem;
  }

  /* Projects */
  .projects-grid {
    grid-template-columns: 1fr;
  }

  /* Case study */
  .case-study-grid {
    grid-template-columns: 1fr;
  }

  .case-study.open {
    max-height: 2400px;
  }

  /* About */
  .about-grid {
    grid-template-columns: 1fr;
    gap: 2rem;
  }
}

@media (min-width: 769px) and (max-width: 1024px) {
  .projects-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

/* =========================
   16. UTILITY
   ========================= */
.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;
}