/* ===========================
   SoftTacWorld Challenge Site
   Premium Edition — Pure CSS
   =========================== */

/* --- Custom Properties --- */
:root {
  --color-primary: #2196F3;
  --color-primary-dark: #1565C0;
  --color-primary-light: #E3F2FD;
  --color-accent: #42A5F5;
  --color-accent-hover: #1E88E5;
  --color-highlight: #f0c840;
  --color-highlight-soft: #fef9e7;

  --color-bg: #ffffff;
  --color-bg-alt: #f8fafb;
  --color-text: #1a1a2e;
  --color-text-soft: #506070;
  --color-text-muted: #8a99a8;
  --color-border: #e8edf2;
  --color-border-light: #f0f4f7;

  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'SF Mono', monospace;
  --font-display: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;

  --nav-height: 4rem;
  --section-padding: 6rem 2rem;
  --container-max: 1120px;

  --shadow-xs: 0 1px 3px rgba(33, 150, 243, 0.04);
  --shadow-sm: 0 2px 8px rgba(33, 150, 243, 0.05), 0 1px 2px rgba(0,0,0,0.03);
  --shadow-md: 0 8px 30px rgba(33, 150, 243, 0.08), 0 2px 6px rgba(0,0,0,0.03);
  --shadow-lg: 0 20px 60px rgba(33, 150, 243, 0.10), 0 4px 12px rgba(0,0,0,0.04);
  --shadow-glow: 0 0 30px rgba(66, 165, 245, 0.15);

  --radius-xs: 4px;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --radius-xl: 28px;

  --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 0.4s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-spring: 0.5s cubic-bezier(0.34, 1.56, 0.64, 1);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--nav-height) + 1rem);
}

body {
  font-family: var(--font-sans);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-feature-settings: 'cv02', 'cv03', 'cv04', 'cv11';
  overflow-x: hidden;
}

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

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

::selection {
  background: rgba(33, 150, 243, 0.15);
  color: var(--color-primary-dark);
}

/* --- Container --- */
.container {
  max-width: var(--container-max);
  margin: 0 auto;
  width: 100%;
}

/* --- Navbar --- */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(21, 101, 192, 0.88);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  z-index: 1000;
  display: flex;
  align-items: center;
  border-bottom: 1px solid rgba(255, 255, 255, 0.06);
  transition: background var(--transition-base), box-shadow var(--transition-base);
}

.navbar.is-scrolled {
  background: rgba(21, 101, 192, 0.95);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.12);
}

.nav-container {
  max-width: 1280px;
  margin: 0 auto;
  width: 100%;
  padding: 0 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-brand {
  font-size: 1.2rem;
  font-weight: 750;
  color: #fff;
  letter-spacing: -0.03em;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.nav-brand::before {
  content: '';
  display: inline-block;
  width: 8px;
  height: 8px;
  background: var(--color-highlight);
  border-radius: 50%;
  box-shadow: 0 0 8px rgba(240, 200, 64, 0.5);
}
.nav-brand:hover {
  color: var(--color-highlight);
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: 0.15rem;
}

.nav-link {
  color: rgba(255, 255, 255, 0.75);
  font-size: 0.82rem;
  font-weight: 500;
  padding: 0.45rem 0.85rem;
  border-radius: 6px;
  transition: all var(--transition-fast);
  position: relative;
  letter-spacing: 0.01em;
}
.nav-link:hover {
  color: #fff;
  background: rgba(255, 255, 255, 0.08);
}
.nav-link.is-active {
  color: #fff;
  background: rgba(255, 255, 255, 0.1);
}
.nav-link.is-active::after {
  content: '';
  position: absolute;
  bottom: 2px;
  left: 50%;
  transform: translateX(-50%);
  width: 16px;
  height: 2px;
  background: var(--color-highlight);
  border-radius: 1px;
}

/* Mobile nav toggle */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
  z-index: 10;
}
.nav-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  background: #fff;
  border-radius: 2px;
  transition: transform var(--transition-base), opacity var(--transition-fast);
  transform-origin: center;
}
.nav-toggle.is-active span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}
.nav-toggle.is-active span:nth-child(2) {
  opacity: 0;
}
.nav-toggle.is-active span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

/* --- Hero --- */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: calc(var(--nav-height) + 3rem) 2rem 5rem;
  background: linear-gradient(160deg, #0d2137 0%, #1256a0 25%, #2196F3 50%, #42A5F5 80%, #64B5F6 100%);
  overflow: hidden;
}

/* Animated background orbs */
.hero::before {
  content: '';
  position: absolute;
  width: 600px;
  height: 600px;
  top: -10%;
  right: -10%;
  background: radial-gradient(circle, rgba(240, 200, 64, 0.08) 0%, transparent 70%);
  border-radius: 50%;
  animation: float-orb 20s ease-in-out infinite;
}
.hero::after {
  content: '';
  position: absolute;
  width: 500px;
  height: 500px;
  bottom: -15%;
  left: -5%;
  background: radial-gradient(circle, rgba(66, 165, 245, 0.12) 0%, transparent 70%);
  border-radius: 50%;
  animation: float-orb 25s ease-in-out infinite reverse;
}

@keyframes float-orb {
  0%, 100% { transform: translate(0, 0) scale(1); }
  25% { transform: translate(30px, -20px) scale(1.05); }
  50% { transform: translate(-20px, 20px) scale(0.95); }
  75% { transform: translate(10px, 30px) scale(1.02); }
}

/* Grid pattern overlay */
.hero-grid-overlay {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(255,255,255,0.02) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,0.02) 1px, transparent 1px);
  background-size: 60px 60px;
  pointer-events: none;
}

.hero-content {
  position: relative;
  z-index: 2;
  max-width: 820px;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.15);
  color: rgba(255, 255, 255, 0.9);
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.4rem 1.2rem;
  border-radius: 2rem;
  margin-bottom: 2rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  backdrop-filter: blur(4px);
}

.hero-title {
  font-size: clamp(3rem, 9vw, 5rem);
  font-weight: 820;
  color: #fff;
  letter-spacing: -0.04em;
  line-height: 1.05;
  margin-bottom: 1rem;
  background: linear-gradient(135deg, #ffffff 0%, rgba(255,255,255,0.85) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-tagline {
  font-size: clamp(1.15rem, 3vw, 1.5rem);
  color: rgba(255, 255, 255, 0.9);
  font-weight: 500;
  margin-bottom: 0.5rem;
  letter-spacing: -0.01em;
}

.hero-subtitle {
  font-size: 1rem;
  color: rgba(255, 255, 255, 0.6);
  margin-bottom: 3rem;
  font-weight: 400;
}

.hero-info-cards {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.75rem;
  margin-bottom: 3rem;
}

.info-card {
  background: rgba(255, 255, 255, 0.06);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-md);
  padding: 1.25rem 0.75rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.35rem;
  transition: all var(--transition-base);
  backdrop-filter: blur(4px);
}

.info-card:hover {
  background: rgba(255, 255, 255, 0.1);
  border-color: rgba(255, 255, 255, 0.2);
  transform: translateY(-2px);
}

.info-card .info-icon {
  font-size: 1.4rem;
  line-height: 1;
}

.info-card .info-label {
  font-size: 0.65rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: rgba(255, 255, 255, 0.5);
  font-weight: 500;
}

.info-card .info-value {
  font-size: 0.88rem;
  font-weight: 650;
  color: #fff;
  line-height: 1.25;
  overflow-wrap: anywhere;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.45rem;
  font-size: 0.88rem;
  font-weight: 600;
  padding: 0.75rem 1.75rem;
  border-radius: var(--radius-sm);
  border: 1.5px solid transparent;
  cursor: pointer;
  transition: all var(--transition-base);
  letter-spacing: 0.01em;
  white-space: nowrap;
}
.btn:hover {
  transform: translateY(-1px);
}
.btn:active {
  transform: translateY(0);
}

.btn-primary {
  background: var(--color-highlight);
  color: var(--color-primary-dark);
  border-color: var(--color-highlight);
  box-shadow: 0 2px 12px rgba(240, 200, 64, 0.2);
}
.btn-primary:hover {
  background: #e8c020;
  color: var(--color-primary-dark);
  box-shadow: 0 6px 24px rgba(240, 200, 64, 0.35);
}

.btn-outline {
  background: transparent;
  color: #fff;
  border-color: rgba(255, 255, 255, 0.3);
}
.btn-outline:hover {
  background: rgba(255, 255, 255, 0.08);
  color: #fff;
  border-color: rgba(255, 255, 255, 0.5);
}

/* Section context buttons */
.section .btn-primary {
  color: #fff;
  background: var(--color-primary);
  border-color: var(--color-primary);
  box-shadow: 0 2px 12px rgba(33, 150, 243, 0.15);
}
.section .btn-primary:hover {
  background: var(--color-primary-dark);
  border-color: var(--color-primary-dark);
  box-shadow: 0 6px 24px rgba(33, 150, 243, 0.25);
}

.section .btn-outline {
  color: var(--color-primary);
  border-color: var(--color-border);
  background: var(--color-bg);
}
.section .btn-outline:hover {
  background: var(--color-primary-light);
  border-color: var(--color-primary);
  color: var(--color-primary-dark);
}

/* --- Sections --- */
.section {
  padding: var(--section-padding);
  position: relative;
}

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

/* Subtle top border accent for alternating sections */
.section-alt::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: min(80%, 600px);
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--color-border), transparent);
}

.section-title {
  font-size: clamp(1.85rem, 4vw, 2.5rem);
  font-weight: 750;
  color: var(--color-primary-dark);
  text-align: center;
  margin-bottom: 0.6rem;
  letter-spacing: -0.03em;
  line-height: 1.2;
}

.section-lead {
  text-align: center;
  color: var(--color-text-soft);
  font-size: 1.05rem;
  max-width: 580px;
  margin: 0 auto 3.5rem;
  line-height: 1.6;
}

/* --- Overview --- */
.overview-grid {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 4rem;
  align-items: center;
  margin-top: 2rem;
}

.overview-text p {
  color: var(--color-text-soft);
  margin-bottom: 1.25rem;
  line-height: 1.75;
  font-size: 0.95rem;
}

.overview-text-wide {
  max-width: 880px;
  margin: 0 auto;
  text-align: center;
}

.definition-block {
  margin-top: 1.75rem;
  padding: 1.75rem 2rem 1.5rem;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-top: 3px solid var(--color-primary);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  text-align: center;
}

.definition-formula {
  font-family: var(--font-display);
  color: var(--color-text);
}

.definition-line {
  font-size: 1.05rem;
  letter-spacing: 0.01em;
  line-height: 1.9;
}

.definition-main {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--color-primary-dark);
}

.definition-note {
  max-width: 640px;
  margin: 1.1rem auto 0;
  padding-top: 1rem;
  border-top: 1px solid var(--color-border-light);
  font-family: var(--font-sans);
  font-size: 0.86rem;
  line-height: 1.7;
  color: var(--color-text-soft);
  text-align: left;
}

.overview-figure {
  background: linear-gradient(135deg, var(--color-bg-alt), #f0f7ff);
  border-radius: var(--radius-lg);
  padding: 2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 280px;
  border: 1px solid var(--color-border-light);
  box-shadow: var(--shadow-sm);
}

.overview-figure img {
  border-radius: var(--radius-sm);
}

.overview-img {
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
  box-shadow: var(--shadow-md);
}

.overview-visual {
  width: min(100%, 1280px);
  margin: 3rem auto 0;
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-lg);
}

.overview-visual img {
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: cover;
  background: #fff;
}

/* Use for infographic-style figures (with embedded titles/text) that must
   never be cropped — shows the full image, letterboxed if needed. */
.overview-visual--contain img {
  aspect-ratio: auto;
  object-fit: contain;
}

.overview-visual figcaption {
  padding: 0.9rem 1.25rem 1rem;
  text-align: center;
  color: var(--color-text-soft);
  font-size: 0.86rem;
  line-height: 1.5;
  border-top: 1px solid var(--color-border-light);
}

.benchmark-visual {
  margin: 2rem auto 3.25rem;
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-md);
}

.benchmark-visual img {
  width: 100%;
  aspect-ratio: 16 / 9;
  object-fit: contain;
  background: #fff;
}

.benchmark-visual figcaption {
  padding: 0.85rem 1.25rem 1rem;
  text-align: center;
  color: var(--color-text-soft);
  font-size: 0.84rem;
  line-height: 1.5;
  border-top: 1px solid var(--color-border-light);
}

/* Placeholder for missing images */
.placeholder-img {
  width: 100%;
  min-height: 200px;
  background: linear-gradient(135deg, var(--color-primary-light) 0%, #f5f9ff 50%, var(--color-bg-alt) 100%);
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  font-size: 0.82rem;
  border: 1.5px dashed var(--color-border);
  font-weight: 500;
}

/* --- Task Cards --- */
.suite-group {
  margin-top: 2.75rem;
}

.suite-group:first-of-type {
  margin-top: 2rem;
}

.suite-group-title {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-primary-dark);
  text-align: center;
  margin-bottom: 0.35rem;
}

.suite-group-lead {
  max-width: 680px;
  margin: 0 auto 1.5rem;
  text-align: center;
  color: var(--color-text-soft);
  font-size: 0.92rem;
}

.task-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.25rem;
  margin-top: 2.5rem;
}

.suite-group .task-grid {
  margin-top: 0;
}

.task-grid-reference {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  max-width: 760px;
  margin-left: auto;
  margin-right: auto;
}

.task-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: all var(--transition-base);
  position: relative;
}
.task-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  opacity: 0;
  transition: opacity var(--transition-base);
}
.task-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: transparent;
}
.task-card:hover::before {
  opacity: 1;
}

.task-card-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 1.25rem 1.25rem 0.5rem;
}

.task-id {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 2.25rem;
  width: auto;
  height: 2.25rem;
  padding: 0 0.5rem;
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  color: #fff;
  font-size: 0.72rem;
  font-weight: 700;
  border-radius: 999px;
  flex-shrink: 0;
  box-shadow: 0 2px 8px rgba(33, 150, 243, 0.2);
}

.task-card-header h3 {
  font-size: 0.95rem;
  font-weight: 650;
  color: var(--color-text);
  line-height: 1.3;
}

.task-card .task-img {
  width: calc(100% - 2.5rem);
  margin: 0.75rem auto;
  height: 130px;
  object-fit: cover;
  border-radius: var(--radius-sm);
}

.task-video {
  display: block;
  width: calc(100% - 2.5rem);
  aspect-ratio: 16 / 9;
  margin: 0.75rem auto;
  background: #f5f8fb;
  border-radius: var(--radius-sm);
  object-fit: contain;
  box-shadow: var(--shadow-xs);
}

.task-card p {
  padding: 0 1.25rem;
  font-size: 0.84rem;
  color: var(--color-text-soft);
  line-height: 1.55;
}

.task-tag {
  display: inline-block;
  margin: 0.75rem 1.25rem 1.25rem;
  font-size: 0.68rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 0.3rem 0.75rem;
  border-radius: 2rem;
  background: var(--color-primary-light);
  color: var(--color-primary);
}

/* --- Dataset Stats --- */
.dataset-stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.25rem;
  margin: 2.5rem 0 3.5rem;
}

.stat-card {
  text-align: center;
  padding: 2rem 1rem;
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  transition: all var(--transition-base);
  position: relative;
  overflow: hidden;
}

.stat-card::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  transform: scaleX(0);
  transition: transform var(--transition-base);
}

.stat-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.stat-card:hover::after {
  transform: scaleX(1);
}

.stat-num {
  display: block;
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--color-primary);
  letter-spacing: -0.04em;
  line-height: 1.1;
}

.stat-label {
  display: block;
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-top: 0.4rem;
  font-weight: 550;
  line-height: 1.35;
}

.dataset-details {
  max-width: 680px;
  margin: 0 auto;
  text-align: center;
}

.dataset-details h3 {
  font-size: 1.2rem;
  font-weight: 650;
  margin-bottom: 0.75rem;
  color: var(--color-text);
}

.dataset-details p {
  color: var(--color-text-soft);
  margin-bottom: 2rem;
  line-height: 1.75;
  font-size: 0.95rem;
}

.download-links {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  justify-content: center;
}

/* --- Timeline --- */
.timeline {
  position: relative;
  max-width: 620px;
  margin: 2.5rem auto 0;
  padding-left: 2.5rem;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 6px;
  top: 8px;
  bottom: 8px;
  width: 2px;
  background: linear-gradient(180deg, var(--color-primary), var(--color-accent), var(--color-border));
  border-radius: 2px;
}

.timeline-item {
  position: relative;
  padding-bottom: 2.25rem;
  padding-left: 1.75rem;
}

.timeline-item:last-child {
  padding-bottom: 0;
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: -2.5rem;
  top: 4px;
  width: 14px;
  height: 14px;
  background: var(--color-bg);
  border: 3px solid var(--color-primary);
  border-radius: 50%;
  z-index: 1;
  transition: all var(--transition-base);
}

.timeline-item:hover::before {
  transform: scale(1.2);
  box-shadow: 0 0 0 4px rgba(33, 150, 243, 0.1);
}

.timeline-item.is-current::before {
  background: var(--color-highlight);
  border-color: var(--color-highlight);
  box-shadow: 0 0 0 5px rgba(240, 200, 64, 0.2), 0 0 15px rgba(240, 200, 64, 0.3);
}

.timeline-date {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--color-primary);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 0.3rem;
}

.timeline-content h4 {
  font-size: 1rem;
  font-weight: 650;
  margin-bottom: 0.2rem;
  color: var(--color-text);
}

.timeline-content p {
  font-size: 0.87rem;
  color: var(--color-text-soft);
  line-height: 1.5;
}

/* --- Rules --- */
.rules-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  margin-top: 2.5rem;
}

.rule-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: 2rem;
  transition: box-shadow var(--transition-base);
}

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

.rule-card h3 {
  font-size: 1.1rem;
  font-weight: 650;
  margin-bottom: 1.25rem;
  color: var(--color-text);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.rule-card h3::before {
  content: '';
  display: inline-block;
  width: 4px;
  height: 20px;
  background: linear-gradient(180deg, var(--color-primary), var(--color-accent));
  border-radius: 2px;
}

.metrics-table {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0;
  font-size: 0.84rem;
  border-radius: var(--radius-sm);
  overflow: hidden;
  border: 1px solid var(--color-border-light);
}

.metrics-table th {
  background: var(--color-primary-light);
  color: var(--color-primary-dark);
  font-weight: 600;
  text-align: left;
  padding: 0.7rem 1rem;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.metrics-table td {
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--color-border-light);
  color: var(--color-text-soft);
}

.metrics-table tr:last-child td {
  border-bottom: none;
}

.metrics-table code {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  background: var(--color-primary-light);
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
  color: var(--color-primary-dark);
  font-weight: 550;
}

.rule-card ul {
  list-style: none;
  padding: 0;
}

.rule-card ul li {
  padding: 0.6rem 0;
  padding-left: 1.5rem;
  position: relative;
  font-size: 0.88rem;
  color: var(--color-text-soft);
  border-bottom: 1px solid var(--color-border-light);
  line-height: 1.5;
}

.rule-card ul li:last-child {
  border-bottom: none;
}

.rule-card ul li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 50%;
  transform: translateY(-50%);
  width: 6px;
  height: 6px;
  background: var(--color-accent);
  border-radius: 50%;
}

.formula-block,
.code-block {
  background: linear-gradient(135deg, var(--color-primary-light), #f7fbff);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-sm);
  color: var(--color-primary-dark);
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.75;
  padding: 1rem 1.1rem;
  overflow-x: auto;
}

.formula-block {
  margin-bottom: 1rem;
}

.code-block {
  margin: 0;
  white-space: pre;
}

.rule-note {
  color: var(--color-text-soft);
  font-size: 0.88rem;
  line-height: 1.7;
}

/* --- Submission Steps --- */
.submission-steps {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.5rem;
  margin-top: 2.5rem;
  position: relative;
}

/* Connecting line between steps */
.submission-steps::before {
  content: '';
  position: absolute;
  top: 1.5rem;
  left: calc(12.5% + 0.75rem);
  right: calc(12.5% + 0.75rem);
  height: 2px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  opacity: 0.3;
  z-index: 0;
}

.step {
  text-align: center;
  padding: 1.5rem 1rem;
  position: relative;
  z-index: 1;
}

.step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 3.25rem;
  height: 3.25rem;
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  color: #fff;
  font-size: 1.2rem;
  font-weight: 700;
  border-radius: 50%;
  margin-bottom: 1.25rem;
  box-shadow: 0 4px 16px rgba(33, 150, 243, 0.2);
  transition: all var(--transition-base);
}

.step:hover .step-num {
  transform: scale(1.1);
  box-shadow: 0 6px 24px rgba(33, 150, 243, 0.3);
}

.step h4 {
  font-size: 0.95rem;
  font-weight: 650;
  margin-bottom: 0.5rem;
  color: var(--color-text);
}

.step p {
  font-size: 0.83rem;
  color: var(--color-text-soft);
  line-height: 1.55;
}

.submission-details {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 2rem;
  margin-top: 2.75rem;
}

/* --- Leaderboard --- */
.leaderboard-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  justify-content: center;
  margin: 2.5rem 0 1.75rem;
}

.tab {
  padding: 0.55rem 1.35rem;
  font-size: 0.82rem;
  font-weight: 600;
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  color: var(--color-text-soft);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.tab:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  background: rgba(33, 150, 243, 0.04);
}

.tab.active {
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  border-color: transparent;
  color: #fff;
  box-shadow: 0 2px 10px rgba(33, 150, 243, 0.2);
}

.table-container {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.leaderboard-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.84rem;
  min-width: 600px;
}

.leaderboard-table th {
  background: linear-gradient(180deg, var(--color-primary-light), #f0f8fa);
  color: var(--color-primary-dark);
  font-weight: 650;
  text-align: left;
  padding: 0.85rem 1.1rem;
  white-space: nowrap;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.leaderboard-table td {
  padding: 0.85rem 1.1rem;
  border-bottom: 1px solid var(--color-border-light);
  color: var(--color-text-soft);
}

.leaderboard-table tbody tr {
  transition: background var(--transition-fast);
}

.leaderboard-table tbody tr:hover {
  background: var(--color-bg-alt);
}

.leaderboard-baseline {
  font-style: italic;
  background: var(--color-bg-alt);
}

.leaderboard-note {
  margin-top: 1rem;
  text-align: center;
  color: var(--color-text-soft);
  font-size: 0.86rem;
}

.rank-gold td:first-child,
.rank-silver td:first-child,
.rank-bronze td:first-child {
  font-weight: 700;
}

.rank-gold {
  background: rgba(240, 200, 64, 0.06);
}

.rank-silver {
  background: rgba(192, 192, 192, 0.06);
}

.rank-bronze {
  background: rgba(205, 127, 50, 0.04);
}

/* --- Organizers --- */
.organizer-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  gap: 2.5rem;
  margin-top: 2.5rem;
  text-align: center;
}

.organizer-card {
  transition: transform var(--transition-base);
}

.organizer-card:hover {
  transform: translateY(-3px);
}

.organizer-card img {
  width: 96px;
  height: 96px;
  border-radius: 50%;
  object-fit: cover;
  margin: 0 auto 0.85rem;
  border: 3px solid var(--color-border-light);
  transition: all var(--transition-base);
  box-shadow: var(--shadow-sm);
}

.organizer-card:hover img {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 4px rgba(33, 150, 243, 0.1), var(--shadow-md);
}

.organizer-card h4 {
  font-size: 0.88rem;
  font-weight: 600;
  margin-bottom: 0.15rem;
}

.organizer-card h4 a {
  color: var(--color-text);
  transition: color var(--transition-fast);
}
.organizer-card h4 a:hover {
  color: var(--color-accent);
}

.organizer-card .affiliation {
  font-size: 0.75rem;
  color: var(--color-text-muted);
  line-height: 1.4;
}

/* --- Sponsors --- */
.sponsor-grid {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 3rem;
  margin-top: 2.5rem;
}

.sponsor-logo img {
  height: 48px;
  width: auto;
  filter: grayscale(100%);
  opacity: 0.5;
  transition: all var(--transition-base);
}

.sponsor-logo:hover img {
  filter: grayscale(0%);
  opacity: 1;
  transform: scale(1.05);
}

/* --- Contact / FAQ --- */
.contact-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 3.5rem;
  margin-top: 2.5rem;
  align-items: start;
}

.faq details {
  border-bottom: 1px solid var(--color-border-light);
  padding: 1.1rem 0;
  transition: background var(--transition-fast);
}

.faq details[open] {
  padding-bottom: 1.25rem;
}

.faq details summary {
  font-weight: 600;
  font-size: 0.92rem;
  cursor: pointer;
  color: var(--color-text);
  list-style: none;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  transition: color var(--transition-fast);
}

.faq details summary:hover {
  color: var(--color-accent);
}

.faq details summary::-webkit-details-marker {
  display: none;
}

.faq details summary::before {
  content: '+';
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.6rem;
  height: 1.6rem;
  border-radius: 50%;
  background: var(--color-primary-light);
  color: var(--color-primary);
  font-size: 1rem;
  font-weight: 700;
  flex-shrink: 0;
  transition: all var(--transition-base);
}

.faq details[open] summary::before {
  content: '−';
  background: var(--color-primary);
  color: #fff;
  transform: rotate(0deg);
}

.faq details p {
  margin-top: 0.85rem;
  font-size: 0.88rem;
  color: var(--color-text-soft);
  line-height: 1.7;
  padding-left: 2.35rem;
}

.contact-info {
  padding: 2rem;
  background: linear-gradient(135deg, var(--color-primary-light), #f0f7ff);
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border-light);
  height: fit-content;
  position: sticky;
  top: calc(var(--nav-height) + 2rem);
}

.contact-info h3 {
  font-size: 1.05rem;
  font-weight: 650;
  margin-bottom: 1.25rem;
  color: var(--color-primary-dark);
}

.contact-info p {
  font-size: 0.88rem;
  color: var(--color-text-soft);
  margin-bottom: 0.85rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

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

/* --- Footer --- */
.footer {
  background: var(--color-primary-dark);
  color: rgba(255, 255, 255, 0.6);
  text-align: center;
  padding: 3.5rem 2rem 2.5rem;
  font-size: 0.82rem;
  letter-spacing: 0.01em;
}

.footer-logos {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 2rem;
  margin-bottom: 1.25rem;
}

.footer-logo {
  height: 80px;
  width: auto;
  filter: brightness(0) invert(1);
  opacity: 0.9;
  transition: opacity var(--transition-base);
}

.footer-logo:hover {
  opacity: 1;
}

.footer-logo-divider {
  font-size: 1.5rem;
  color: rgba(255, 255, 255, 0.35);
  font-weight: 300;
}

.footer-label {
  font-size: 0.95rem;
  font-weight: 600;
  color: rgba(255, 255, 255, 0.8);
  margin-bottom: 1rem;
  letter-spacing: 0.04em;
}

.footer a {
  color: rgba(255, 255, 255, 0.85);
  transition: color var(--transition-fast);
}

.footer a:hover {
  color: var(--color-highlight);
}

/* --- Back to Top --- */
#back-to-top {
  display: none;
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  width: 2.75rem;
  height: 2.75rem;
  background: var(--color-primary);
  color: #fff;
  border: none;
  border-radius: 50%;
  font-size: 1.1rem;
  cursor: pointer;
  box-shadow: var(--shadow-md);
  transition: all var(--transition-base);
  z-index: 900;
  opacity: 0;
  transform: translateY(10px);
}
#back-to-top.is-visible {
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 1;
  transform: translateY(0);
}
#back-to-top:hover {
  background: var(--color-primary-dark);
  transform: translateY(-3px);
  box-shadow: var(--shadow-lg);
}

/* --- Scroll Reveal --- */
.reveal {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.7s cubic-bezier(0.4, 0, 0.2, 1), transform 0.7s cubic-bezier(0.4, 0, 0.2, 1);
}
.reveal.is-visible {
  opacity: 1;
  transform: translateY(0);
}

/* Staggered reveals for grid children */
.reveal.is-visible .task-card,
.reveal.is-visible .stat-card,
.reveal.is-visible .step,
.reveal.is-visible .timeline-item {
  animation: stagger-in 0.5s cubic-bezier(0.4, 0, 0.2, 1) backwards;
}
.reveal.is-visible .task-card:nth-child(1),
.reveal.is-visible .stat-card:nth-child(1),
.reveal.is-visible .step:nth-child(1),
.reveal.is-visible .timeline-item:nth-child(1) { animation-delay: 0s; }
.reveal.is-visible .task-card:nth-child(2),
.reveal.is-visible .stat-card:nth-child(2),
.reveal.is-visible .step:nth-child(2),
.reveal.is-visible .timeline-item:nth-child(2) { animation-delay: 0.08s; }
.reveal.is-visible .task-card:nth-child(3),
.reveal.is-visible .stat-card:nth-child(3),
.reveal.is-visible .step:nth-child(3),
.reveal.is-visible .timeline-item:nth-child(3) { animation-delay: 0.16s; }
.reveal.is-visible .task-card:nth-child(4),
.reveal.is-visible .stat-card:nth-child(4),
.reveal.is-visible .step:nth-child(4),
.reveal.is-visible .timeline-item:nth-child(4) { animation-delay: 0.24s; }
.reveal.is-visible .timeline-item:nth-child(5) { animation-delay: 0.32s; }
.reveal.is-visible .timeline-item:nth-child(6) { animation-delay: 0.4s; }

@keyframes stagger-in {
  from {
    opacity: 0;
    transform: translateY(16px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* --- Responsive --- */

/* Wide desktop */
@media (min-width: 1280px) {
  :root {
    --container-max: 1160px;
  }
}

/* Tablet landscape / small desktop */
@media (max-width: 1024px) {
  .nav-menu {
    display: none;
    position: absolute;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: rgba(21, 101, 192, 0.98);
    backdrop-filter: blur(20px);
    flex-direction: column;
    padding: 1rem 2rem 1.5rem;
    gap: 0.2rem;
    border-bottom: 1px solid rgba(255,255,255,0.06);
    animation: nav-slide-down 0.25s ease;
  }
  @keyframes nav-slide-down {
    from { opacity: 0; transform: translateY(-8px); }
    to { opacity: 1; transform: translateY(0); }
  }
  .nav-menu.is-open {
    display: flex;
  }
  .nav-toggle {
    display: flex;
  }
  .nav-link {
    padding: 0.65rem 0.85rem;
    width: 100%;
    border-radius: var(--radius-sm);
  }

  .task-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .task-grid-reference,
  .submission-details {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .submission-steps {
    grid-template-columns: repeat(2, 1fr);
  }
  .submission-steps::before {
    display: none;
  }
}

/* Tablet portrait */
@media (max-width: 768px) {
  :root {
    --section-padding: 4rem 1.5rem;
  }

  .hero {
    padding-top: calc(var(--nav-height) + 2.5rem);
    padding-bottom: 3.5rem;
    min-height: auto;
  }

  .hero-title {
    font-size: clamp(2.25rem, 10vw, 3.5rem);
  }

  .hero-info-cards {
    grid-template-columns: repeat(2, 1fr);
  }

  .overview-grid {
    grid-template-columns: 1fr;
    gap: 2.5rem;
  }

  .definition-block {
    padding: 1.5rem 1.25rem;
  }

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

  .submission-details {
    grid-template-columns: 1fr;
  }

  .contact-grid {
    grid-template-columns: 1fr;
    gap: 2rem;
  }

  .contact-info {
    position: static;
  }

  .dataset-stats {
    grid-template-columns: repeat(2, 1fr);
  }

  .section-title {
    font-size: clamp(1.6rem, 5vw, 2rem);
  }

  .section-lead {
    margin-bottom: 2.5rem;
  }
}

/* Mobile */
@media (max-width: 480px) {
  :root {
    --section-padding: 3.5rem 1.25rem;
  }

  .nav-container {
    padding: 0 1.25rem;
  }

  .hero-info-cards {
    grid-template-columns: 1fr 1fr;
    gap: 0.5rem;
  }

  .info-card {
    padding: 1rem 0.5rem;
  }

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

  .task-grid-reference {
    grid-template-columns: 1fr;
  }

  .submission-steps {
    grid-template-columns: 1fr;
  }

  .dataset-stats {
    grid-template-columns: 1fr 1fr;
  }

  .hero-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .btn {
    justify-content: center;
    padding: 0.8rem 1.5rem;
  }

  .leaderboard-tabs {
    gap: 0.25rem;
  }

  .tab {
    padding: 0.45rem 0.85rem;
    font-size: 0.76rem;
  }

  .timeline {
    padding-left: 2rem;
  }

  .timeline::before {
    left: 4px;
  }

  .timeline-item::before {
    left: -2rem;
  }

  .organizer-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: 1.5rem;
  }
}

/* Small mobile */
@media (max-width: 360px) {
  .hero-info-cards {
    grid-template-columns: 1fr;
  }

  .dataset-stats {
    grid-template-columns: 1fr;
  }

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

/* --- Reduced motion --- */
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  .reveal {
    opacity: 1;
    transform: none;
    transition: none;
  }
  .reveal.is-visible .task-card,
  .reveal.is-visible .stat-card,
  .reveal.is-visible .step,
  .reveal.is-visible .timeline-item {
    animation: none;
  }
  .task-card:hover,
  .stat-card:hover,
  .organizer-card:hover,
  .step:hover .step-num {
    transform: none;
  }
  .hero::before,
  .hero::after {
    animation: none;
  }
  #back-to-top {
    transition: none;
  }
}