/* ============================================
   BD Traffic Signs - Minimalist Academic Design
   Material-inspired, research-focused UI
   ============================================ */

/* Design Tokens */
:root {
  /* Color System */
  --color-primary: #1a73e8;
  --color-primary-dark: #1557b0;
  --color-primary-light: #4285f4;
  --color-accent: #34a853;
  --color-warning: #fbbc04;
  --color-error: #ea4335;
  
  /* Neutrals */
  --color-bg: #ffffff;
  --color-surface: #f8f9fa;
  --color-surface-dark: #f1f3f4;
  --color-border: #dadce0;
  --color-divider: #e8eaed;
  
  /* Text */
  --color-text: #202124;
  --color-text-secondary: #5f6368;
  --color-text-tertiary: #80868b;
  --color-text-inverse: #ffffff;
  
  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Roboto Mono', monospace;
  
  /* Spacing Scale */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-8: 3rem;
  --space-10: 4rem;
  --space-12: 5rem;
  --space-16: 8rem;
  
  /* Elevation */
  --shadow-1: 0 1px 2px 0 rgba(60,64,67,.3), 0 1px 3px 1px rgba(60,64,67,.15);
  --shadow-2: 0 1px 3px 0 rgba(60,64,67,.3), 0 4px 8px 3px rgba(60,64,67,.15);
  --shadow-3: 0 1px 3px 0 rgba(60,64,67,.3), 0 6px 10px 4px rgba(60,64,67,.15);
  
  /* Radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --radius-full: 9999px;
  
  /* Transitions */
  --ease-out: cubic-bezier(0.4, 0, 0.2, 1);
  --duration-fast: 150ms;
  --duration-normal: 250ms;
  --duration-slow: 400ms;
  
  /* Layout */
  --max-width: 1200px;
  --content-width: 800px;
  --nav-height: 64px;
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: var(--nav-height);
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.6;
}

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

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

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

/* Typography */
h1, h2, h3, h4 {
  font-weight: 600;
  line-height: 1.25;
  color: var(--color-text);
}

h1 {
  font-size: 2.5rem;
  letter-spacing: -0.025em;
}

h2 {
  font-size: 1.75rem;
  letter-spacing: -0.02em;
}

h3 {
  font-size: 1.25rem;
}

p {
  color: var(--color-text-secondary);
}

/* Layout */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.container--narrow {
  max-width: var(--content-width);
}

/* Navigation */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-border);
  z-index: 1000;
  transition: box-shadow var(--duration-normal) var(--ease-out);
}

.nav.scrolled {
  box-shadow: var(--shadow-1);
}

.nav__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.nav__brand {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-weight: 600;
  font-size: 1.125rem;
  color: var(--color-text);
}

.nav__brand svg {
  width: 28px;
  height: 28px;
  color: var(--color-primary);
}

.nav__links {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  list-style: none;
}

.nav__link {
  padding: var(--space-2) var(--space-3);
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-out);
}

.nav__link:hover,
.nav__link.active {
  color: var(--color-primary);
  background: rgba(26, 115, 232, 0.08);
}

.nav__toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: var(--space-2);
  background: none;
  border: none;
  cursor: pointer;
}

.nav__toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  border-radius: var(--radius-full);
  transition: all var(--duration-normal) var(--ease-out);
}

/* Hero Section */
.hero {
  padding: calc(var(--nav-height) + var(--space-16)) 0 var(--space-16);
  background: linear-gradient(180deg, var(--color-surface) 0%, var(--color-bg) 100%);
}

.hero__content {
  text-align: center;
  max-width: 900px;
  margin: 0 auto;
}

.hero__badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  background: rgba(26, 115, 232, 0.1);
  color: var(--color-primary);
  font-size: 0.875rem;
  font-weight: 500;
  border-radius: var(--radius-full);
  margin-bottom: var(--space-5);
}

.hero__title {
  font-size: clamp(2rem, 5vw, 3rem);
  margin-bottom: var(--space-4);
  color: var(--color-text);
}

.hero__subtitle {
  font-size: 1.25rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--space-6);
  max-width: 700px;
  margin-left: auto;
  margin-right: auto;
}

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

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-5);
  font-family: inherit;
  font-size: 0.9375rem;
  font-weight: 500;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-out);
}

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

.btn--primary:hover {
  background: var(--color-primary-dark);
  color: var(--color-text-inverse);
  box-shadow: var(--shadow-1);
}

.btn--secondary {
  background: var(--color-surface);
  color: var(--color-primary);
  border: 1px solid var(--color-border);
}

.btn--secondary:hover {
  background: var(--color-surface-dark);
  color: var(--color-primary);
}

.btn svg {
  width: 18px;
  height: 18px;
}

/* Metrics Bar */
.metrics {
  padding: var(--space-8) 0;
  border-bottom: 1px solid var(--color-divider);
}

.metrics__grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-6);
}

.metric {
  text-align: center;
}

.metric__value {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--color-primary);
  line-height: 1;
  margin-bottom: var(--space-2);
}

.metric__value--accent {
  color: var(--color-accent);
}

.metric__label {
  font-size: 0.875rem;
  color: var(--color-text-tertiary);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

/* Sections */
.section {
  padding: var(--space-12) 0;
}

.section--alt {
  background: var(--color-surface);
}

.section__header {
  text-align: center;
  margin-bottom: var(--space-8);
}

.section__title {
  margin-bottom: var(--space-3);
}

.section__subtitle {
  max-width: 600px;
  margin: 0 auto;
  color: var(--color-text-secondary);
}

/* Cards */
.card {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  transition: box-shadow var(--duration-normal) var(--ease-out);
}

.card:hover {
  box-shadow: var(--shadow-2);
}

.card__icon {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(26, 115, 232, 0.1);
  color: var(--color-primary);
  border-radius: var(--radius-md);
  margin-bottom: var(--space-4);
}

.card__title {
  font-size: 1.125rem;
  margin-bottom: var(--space-2);
}

.card__text {
  font-size: 0.9375rem;
  color: var(--color-text-secondary);
}

/* Highlights Grid */
.highlights {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-5);
}

/* Results Section */
.results__tabs {
  display: flex;
  gap: var(--space-2);
  margin-bottom: var(--space-6);
  border-bottom: 1px solid var(--color-border);
  padding-bottom: var(--space-1);
  overflow-x: auto;
}

.tab-btn {
  padding: var(--space-3) var(--space-4);
  font-family: inherit;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text-secondary);
  background: none;
  border: none;
  border-bottom: 2px solid transparent;
  cursor: pointer;
  white-space: nowrap;
  transition: all var(--duration-fast) var(--ease-out);
}

.tab-btn:hover {
  color: var(--color-primary);
}

.tab-btn.active {
  color: var(--color-primary);
  border-bottom-color: var(--color-primary);
}

.tab-panel {
  display: none;
}

.tab-panel.active {
  display: block;
  animation: fadeIn var(--duration-normal) var(--ease-out);
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.result-figure {
  text-align: center;
}

.result-figure img {
  max-width: 100%;
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
  margin: 0 auto;
}

.result-figure figcaption {
  margin-top: var(--space-4);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
}

/* Data Table */
.data-table {
  width: 100%;
  border-collapse: collapse;
  margin: var(--space-6) 0;
  font-size: 0.9375rem;
}

.data-table th,
.data-table td {
  padding: var(--space-3) var(--space-4);
  text-align: left;
  border-bottom: 1px solid var(--color-divider);
}

.data-table th {
  font-weight: 600;
  color: var(--color-text);
  background: var(--color-surface);
}

.data-table tr:hover td {
  background: var(--color-surface);
}

.data-table .highlight {
  color: var(--color-primary);
  font-weight: 600;
}

/* Demo Section */
.demo-container {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.demo-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-4) var(--space-5);
  background: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
}

.demo-header__title {
  font-size: 1rem;
  font-weight: 600;
}

.demo-header__link {
  font-size: 0.875rem;
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.demo-frame {
  width: 100%;
  height: 600px;
  border: none;
  background: var(--color-bg);
}

.demo-placeholder {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 400px;
  text-align: center;
  padding: var(--space-6);
}

.demo-placeholder svg {
  width: 64px;
  height: 64px;
  color: var(--color-text-tertiary);
  margin-bottom: var(--space-4);
}

/* Paper Section */
.paper-card {
  display: grid;
  grid-template-columns: 1fr 2fr;
  gap: var(--space-6);
  padding: var(--space-6);
}

.paper-preview {
  background: var(--color-surface-dark);
  border-radius: var(--radius-md);
  padding: var(--space-6);
  display: flex;
  align-items: center;
  justify-content: center;
}

.paper-preview svg {
  width: 80px;
  height: 80px;
  color: var(--color-primary);
}

.paper-info__title {
  font-size: 1.25rem;
  margin-bottom: var(--space-3);
}

.paper-info__authors {
  color: var(--color-text-secondary);
  margin-bottom: var(--space-2);
}

.paper-info__venue {
  font-size: 0.875rem;
  color: var(--color-text-tertiary);
  margin-bottom: var(--space-5);
}

.paper-info__actions {
  display: flex;
  gap: var(--space-3);
  flex-wrap: wrap;
}

/* Dataset Section */
.dataset-stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-4);
  margin-bottom: var(--space-6);
}

.stat-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-4);
  text-align: center;
}

.stat-card__value {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--color-text);
}

.stat-card__label {
  font-size: 0.8125rem;
  color: var(--color-text-tertiary);
  margin-top: var(--space-1);
}

/* Citation */
.citation-box {
  background: var(--color-text);
  color: var(--color-surface);
  border-radius: var(--radius-lg);
  padding: var(--space-5);
  position: relative;
}

.citation-box pre {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  line-height: 1.7;
  overflow-x: auto;
  white-space: pre-wrap;
  word-break: break-word;
}

.citation-copy {
  position: absolute;
  top: var(--space-4);
  right: var(--space-4);
  padding: var(--space-2) var(--space-3);
  font-size: 0.75rem;
  background: rgba(255, 255, 255, 0.1);
  color: var(--color-surface);
  border: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-out);
}

.citation-copy:hover {
  background: rgba(255, 255, 255, 0.2);
}

/* Footer */
.footer {
  background: var(--color-text);
  color: var(--color-surface);
  padding: var(--space-10) 0 var(--space-6);
}

.footer__grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--space-8);
  margin-bottom: var(--space-8);
}

.footer__brand {
  font-size: 1.125rem;
  font-weight: 600;
  margin-bottom: var(--space-3);
}

.footer__desc {
  color: var(--color-text-tertiary);
  font-size: 0.875rem;
  line-height: 1.6;
}

.footer__title {
  font-size: 0.8125rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-4);
  color: var(--color-text-tertiary);
}

.footer__links {
  list-style: none;
}

.footer__links li {
  margin-bottom: var(--space-2);
}

.footer__links a {
  color: var(--color-surface);
  font-size: 0.875rem;
  opacity: 0.8;
  transition: opacity var(--duration-fast) var(--ease-out);
}

.footer__links a:hover {
  opacity: 1;
  color: var(--color-surface);
}

.footer__bottom {
  padding-top: var(--space-6);
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8125rem;
  color: var(--color-text-tertiary);
}

.footer__social {
  display: flex;
  gap: var(--space-4);
}

.footer__social a {
  color: var(--color-surface);
  opacity: 0.6;
  transition: opacity var(--duration-fast) var(--ease-out);
}

.footer__social a:hover {
  opacity: 1;
}

.footer__social svg {
  width: 20px;
  height: 20px;
}

/* Back to Top */
.back-to-top {
  position: fixed;
  bottom: var(--space-6);
  right: var(--space-6);
  width: 44px;
  height: 44px;
  background: var(--color-primary);
  color: var(--color-text-inverse);
  border: none;
  border-radius: var(--radius-full);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: all var(--duration-normal) var(--ease-out);
  box-shadow: var(--shadow-2);
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--color-primary-dark);
}

.back-to-top svg {
  width: 20px;
  height: 20px;
}

/* Utilities */
.text-center { text-align: center; }
.text-primary { color: var(--color-primary); }
.font-mono { font-family: var(--font-mono); }
.mt-2 { margin-top: var(--space-2); }
.mt-4 { margin-top: var(--space-4); }
.mt-6 { margin-top: var(--space-6); }
.mb-4 { margin-bottom: var(--space-4); }
.mb-6 { margin-bottom: var(--space-6); }

/* Visually Hidden (accessibility) */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}