/* ============================================
   Matthew Fong Portfolio - Main Stylesheet
   Three-panel layout with left nav & right TOC
   ============================================ */

/* CSS Variables */
:root {
  /* Colors - Light, clean palette */
  --color-bg: #FAFAFA;
  --color-bg-alt: #FFFFFF;
  --color-bg-code: #F4F4F5;
  --color-text: #18181B;
  --color-text-secondary: #52525B;
  --color-text-muted: #71717A;
  --color-border: #E4E4E7;
  --color-border-light: #F4F4F5;
  --color-primary: #2563EB;
  --color-primary-hover: #1D4ED8;
  --color-accent: #7C3AED;
  --color-success: #059669;

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

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;

  /* Layout */
  --max-width: 1200px;
  --content-width: 900px;
  --header-height: 64px;
  --sidebar-width: 260px;
  --toc-width: 220px;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 200ms ease;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);

  /* Border radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
}

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

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

body {
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.6;
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  color: var(--color-text);
  margin-bottom: var(--space-md);
}

h1 {
  font-size: 2.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

h2 {
  font-size: 1.75rem;
  letter-spacing: -0.01em;
  margin-top: var(--space-2xl);
}

h3 {
  font-size: 1.25rem;
  margin-top: var(--space-xl);
}

p {
  margin-bottom: var(--space-md);
}

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

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

strong {
  font-weight: 600;
}

code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  background-color: var(--color-bg-code);
  padding: 0.125em 0.375em;
  border-radius: var(--radius-sm);
}

pre {
  background-color: var(--color-bg-code);
  padding: var(--space-lg);
  border-radius: var(--radius-md);
  overflow-x: auto;
  margin: var(--space-lg) 0;
}

pre code {
  background: none;
  padding: 0;
}

/* ============================================
   Header
   ============================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: rgba(250, 250, 250, 0.9);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--color-border);
  height: var(--header-height);
}

.header-container {
  padding: 0 var(--space-lg);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.header-left {
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

.site-logo {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  gap: 0;
}

.logo-text {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--color-text);
  line-height: 1.2;
}

.logo-subtitle {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  line-height: 1.2;
}

.site-logo:hover {
  text-decoration: none;
}

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

.header-links {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
  list-style: none;
}

.header-links a {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  text-decoration: none;
}

.header-links a:hover {
  color: var(--color-text);
  text-decoration: none;
}

.nav-external::after {
  content: ' \2197';
  font-size: 0.75em;
}

/* Sidebar toggle button (for mobile) */
#sidebar-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-sm);
}

.hamburger {
  display: block;
  width: 24px;
  height: 2px;
  background-color: var(--color-text);
  position: relative;
}

.hamburger::before,
.hamburger::after {
  content: '';
  position: absolute;
  width: 100%;
  height: 2px;
  background-color: var(--color-text);
  left: 0;
}

.hamburger::before {
  top: -7px;
}

.hamburger::after {
  bottom: -7px;
}

/* ============================================
   Three-Panel Layout
   ============================================ */
.site-layout {
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr var(--toc-width);
  min-height: calc(100vh - var(--header-height));
}

.main-content {
  min-width: 0; /* Prevent grid blowout */
  min-height: calc(100vh - var(--header-height) - 200px);
}

/* ============================================
   Left Sidebar
   ============================================ */
.sidebar {
  position: sticky;
  top: var(--header-height);
  height: calc(100vh - var(--header-height));
  overflow-y: auto;
  border-right: 1px solid var(--color-border);
  background-color: var(--color-bg-alt);
  padding: var(--space-lg) 0;
  scrollbar-width: thin;
  scrollbar-color: var(--color-border) transparent;
}

.sidebar::-webkit-scrollbar {
  width: 4px;
}

.sidebar::-webkit-scrollbar-track {
  background: transparent;
}

.sidebar::-webkit-scrollbar-thumb {
  background-color: var(--color-border);
  border-radius: 2px;
}

.sidebar-nav {
  padding: 0 var(--space-md);
}

/* Nav list base */
.nav-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-list--root > .nav-item {
  margin-bottom: var(--space-xs);
}

/* Nav item row (for items with toggle) */
.nav-item-row {
  display: flex;
  align-items: center;
  gap: 0;
}

.nav-item-row .nav-link {
  flex: 1;
}

/* Nav link */
.nav-link {
  display: block;
  padding: 6px var(--space-sm);
  font-size: 0.875rem;
  font-weight: 400;
  color: var(--color-text-secondary);
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: color var(--transition-fast), background-color var(--transition-fast);
  line-height: 1.4;
}

.nav-link:hover {
  color: var(--color-text);
  background-color: var(--color-bg);
  text-decoration: none;
}

.nav-link--active {
  color: var(--color-primary);
  font-weight: 500;
  background-color: rgba(37, 99, 235, 0.06);
}

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

/* Section headers (top-level items with children) */
.nav-list--root > .nav-item > .nav-item-row > .nav-link,
.nav-list--root > .nav-item > .nav-link {
  font-weight: 500;
  font-size: 0.875rem;
}

/* Toggle button */
.nav-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  background: none;
  border: none;
  cursor: pointer;
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  transition: color var(--transition-fast), background-color var(--transition-fast);
  flex-shrink: 0;
}

.nav-toggle:hover {
  color: var(--color-text);
  background-color: var(--color-bg);
}

.nav-chevron {
  transition: transform var(--transition-base);
}

.nav-item--open > .nav-item-row > .nav-toggle .nav-chevron {
  transform: rotate(90deg);
}

/* Children lists - indentation */
.nav-list--children {
  padding-left: var(--space-md);
  margin-top: var(--space-xs);
}

.nav-list--grandchildren {
  padding-left: var(--space-md);
  margin-top: var(--space-xs);
}

.nav-list--children .nav-link,
.nav-list--grandchildren .nav-link {
  font-size: 0.8125rem;
  padding: 4px var(--space-sm);
}

/* Sidebar overlay for mobile */
.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background-color: rgba(0, 0, 0, 0.3);
  z-index: 40;
}

.sidebar-overlay--visible {
  display: block;
}

/* ============================================
   Right TOC Sidebar
   ============================================ */
.toc-sidebar {
  position: sticky;
  top: var(--header-height);
  height: calc(100vh - var(--header-height));
  overflow-y: auto;
  padding: var(--space-xl) var(--space-md) var(--space-xl) var(--space-lg);
  border-left: 1px solid var(--color-border);
  scrollbar-width: thin;
  scrollbar-color: var(--color-border) transparent;
}

.toc-sidebar::-webkit-scrollbar {
  width: 4px;
}

.toc-sidebar::-webkit-scrollbar-track {
  background: transparent;
}

.toc-sidebar::-webkit-scrollbar-thumb {
  background-color: var(--color-border);
  border-radius: 2px;
}

.toc-title {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-sm);
}

.toc-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.toc-list--nested {
  padding-left: var(--space-md);
}

.toc-item {
  margin: 0;
}

.toc-link {
  display: block;
  padding: 4px 0 4px var(--space-sm);
  font-size: 0.8125rem;
  color: var(--color-text-muted);
  text-decoration: none;
  border-left: 2px solid transparent;
  transition: color var(--transition-fast), border-color var(--transition-fast);
  line-height: 1.4;
}

.toc-link:hover {
  color: var(--color-text-secondary);
  text-decoration: none;
}

.toc-link--active {
  color: var(--color-primary);
  border-left-color: var(--color-primary);
}

/* ============================================
   Page Layouts
   ============================================ */
.page-hero {
  background-color: var(--color-bg-alt);
  border-bottom: 1px solid var(--color-border);
  padding: var(--space-2xl) var(--space-xl);
}

.page-hero-content {
  max-width: var(--content-width);
}

.page-hero h1 {
  margin-bottom: var(--space-md);
}

.page-hero .lead {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  line-height: 1.5;
}

.page-content {
  max-width: var(--content-width);
  padding: var(--space-2xl) var(--space-xl);
}

/* Home page specific */
.home-hero {
  background: linear-gradient(to bottom, var(--color-bg-alt), var(--color-bg));
  padding: var(--space-3xl) var(--space-xl);
  text-align: center;
}

.home-hero-content {
  max-width: 700px;
  margin: 0 auto;
}

.home-hero h1 {
  font-size: 2.5rem;
  margin-bottom: var(--space-lg);
}

.home-hero .lead {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-xl);
}

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

/* Value pillars on homepage */
.value-pillars {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-lg);
  padding: var(--space-2xl) var(--space-xl);
  max-width: var(--content-width);
  margin: 0 auto;
}

.pillar {
  text-align: center;
  padding: var(--space-lg);
}

.pillar-icon {
  font-size: 1.5rem;
  margin-bottom: var(--space-sm);
  display: block;
}

.pillar h3 {
  font-size: 1rem;
  margin-top: 0;
  margin-bottom: var(--space-sm);
}

.pillar p {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  margin-bottom: 0;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  font-size: 0.9375rem;
  font-weight: 500;
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: all var(--transition-fast);
  cursor: pointer;
  border: none;
}

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

.btn-primary:hover {
  background-color: var(--color-primary-hover);
  color: white;
  text-decoration: none;
}

.btn-secondary {
  background-color: var(--color-bg-alt);
  color: var(--color-text);
  border: 1px solid var(--color-border);
}

.btn-secondary:hover {
  background-color: var(--color-bg);
  border-color: var(--color-text-muted);
  text-decoration: none;
}

/* Sample cards */
.samples-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: var(--space-lg);
  margin: var(--space-xl) 0;
}

.sample-card {
  background-color: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  transition: all var(--transition-base);
  text-decoration: none;
  display: flex;
  flex-direction: column;
}

.sample-card:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-md);
  text-decoration: none;
  transform: translateY(-2px);
}

.sample-card-icon {
  font-size: 2rem;
  margin-bottom: var(--space-md);
}

.sample-card h3 {
  color: var(--color-text);
  margin-top: 0;
  margin-bottom: var(--space-sm);
}

.sample-card p {
  color: var(--color-text-secondary);
  font-size: 0.9375rem;
  margin-bottom: var(--space-md);
  flex-grow: 1;
}

.sample-card .card-link {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-primary);
}

/* Skills tags */
.skills-section {
  background-color: var(--color-bg-alt);
  border-top: 1px solid var(--color-border);
  padding: var(--space-2xl) var(--space-xl);
}

.skills-content {
  max-width: var(--content-width);
  margin: 0 auto;
  text-align: center;
}

.skills-content h2 {
  margin-top: 0;
  margin-bottom: var(--space-lg);
}

.skills-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
  justify-content: center;
}

.skill-tag {
  background-color: var(--color-bg);
  border: 1px solid var(--color-border);
  padding: var(--space-xs) var(--space-md);
  border-radius: 100px;
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

/* Research showcase grid */
.research-showcase {
  margin: var(--space-xl) 0;
}

.showcase-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-lg);
}

.showcase-figure {
  margin: 0;
}

.showcase-figure a {
  display: block;
  border-radius: 6px;
  overflow: hidden;
  border: 1px solid var(--color-border);
  transition: box-shadow 0.2s ease;
}

.showcase-figure a:hover {
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.showcase-figure img {
  width: 100%;
  height: auto;
  display: block;
}

.showcase-figure figcaption {
  margin-top: var(--space-sm);
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  text-align: center;
}

@media (max-width: 600px) {
  .showcase-grid {
    grid-template-columns: 1fr;
  }
}

/* Sample page content */
.sample-meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
  padding-bottom: var(--space-lg);
  border-bottom: 1px solid var(--color-border);
}

.meta-item {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

.meta-label {
  font-weight: 500;
  color: var(--color-text-muted);
}

/* Info boxes */
.info-box {
  background-color: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-left: 4px solid var(--color-primary);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  margin: var(--space-lg) 0;
}

.info-box h4 {
  margin-top: 0;
  margin-bottom: var(--space-sm);
  color: var(--color-primary);
}

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

.info-box.highlight {
  border-left-color: var(--color-accent);
}

.info-box.highlight h4 {
  color: var(--color-accent);
}

.info-box.success {
  border-left-color: var(--color-success);
}

.info-box.success h4 {
  color: var(--color-success);
}

/* Lists */
.page-content ul,
.page-content ol {
  margin-left: var(--space-lg);
  margin-bottom: var(--space-md);
}

.page-content li {
  margin-bottom: var(--space-sm);
}

/* Figures */
.figure {
  margin: var(--space-xl) 0;
}

.figure img {
  width: 100%;
  height: auto;
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
}

.figure-caption {
  margin-top: var(--space-md);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  font-style: italic;
}

.figure-title {
  font-weight: 600;
  color: var(--color-text);
  font-style: normal;
}

/* External link button */
.external-link-box {
  background-color: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  margin: var(--space-xl) 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.external-link-box h4 {
  margin: 0;
}

.external-link-box p {
  margin: 0;
  color: var(--color-text-secondary);
  font-size: 0.9375rem;
}

/* Footer */
.site-footer {
  background-color: var(--color-bg-alt);
  border-top: 1px solid var(--color-border);
  padding: var(--space-2xl) var(--space-lg);
  margin-top: var(--space-3xl);
}

.footer-content {
  max-width: var(--content-width);
  margin: 0 auto;
  text-align: center;
}

.footer-name {
  font-weight: 600;
  font-size: 1.125rem;
  margin-bottom: var(--space-xs);
}

.footer-tagline {
  color: var(--color-text-muted);
  font-size: 0.875rem;
  margin-bottom: var(--space-lg);
}

.footer-links {
  display: flex;
  justify-content: center;
  gap: var(--space-xl);
  margin-bottom: var(--space-lg);
}

.footer-links a {
  color: var(--color-text-secondary);
  font-size: 0.875rem;
}

.footer-copyright {
  color: var(--color-text-muted);
  font-size: 0.8125rem;
}

/* About page */
.about-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-2xl);
}

.experience-item {
  border-left: 2px solid var(--color-border);
  padding-left: var(--space-lg);
  margin-bottom: var(--space-xl);
}

.experience-item h4 {
  margin-top: 0;
  margin-bottom: var(--space-xs);
}

.experience-meta {
  font-size: 0.875rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-sm);
}

/* Download button */
.download-section {
  background-color: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  text-align: center;
  margin: var(--space-xl) 0;
}

/* ============================================
   Responsive - Tablet (no right TOC)
   ============================================ */
@media (max-width: 1280px) {
  .site-layout {
    grid-template-columns: var(--sidebar-width) 1fr;
  }

  .toc-sidebar {
    display: none;
  }
}

/* ============================================
   Responsive - Mobile (sidebar overlay)
   ============================================ */
@media (max-width: 1024px) {
  #sidebar-toggle {
    display: block;
  }

  .site-layout {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: fixed;
    top: var(--header-height);
    left: 0;
    bottom: 0;
    width: var(--sidebar-width);
    z-index: 50;
    transform: translateX(-100%);
    transition: transform var(--transition-base);
    border-right: 1px solid var(--color-border);
    box-shadow: var(--shadow-lg);
  }

  .sidebar--open {
    transform: translateX(0);
  }

  .toc-sidebar {
    display: none;
  }

  .page-hero {
    padding: var(--space-xl) var(--space-lg);
  }

  .page-content {
    padding: var(--space-xl) var(--space-lg);
  }

  .home-hero {
    padding: var(--space-2xl) var(--space-lg);
  }

  .home-hero h1 {
    font-size: 2rem;
  }

  h1 {
    font-size: 2rem;
  }

  h2 {
    font-size: 1.5rem;
  }

  .value-pillars {
    grid-template-columns: 1fr;
    padding: var(--space-xl) var(--space-lg);
  }

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

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

  .footer-links {
    flex-direction: column;
    gap: var(--space-md);
  }

  .header-links {
    display: none;
  }
}

/* ============================================
   Print styles
   ============================================ */
@media print {
  .site-header,
  .site-footer,
  .hero-cta,
  .sidebar,
  .toc-sidebar,
  .sidebar-overlay {
    display: none;
  }

  .site-layout {
    grid-template-columns: 1fr;
  }

  .main-content {
    padding: 0;
  }
}