* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --white: #ffffff;
  --gray-50: #f8fafc;
  --gray-100: #e2e8f0;
  --gray-200: #cbd5e1;
  --gray-300: #94a3b8;
  --gray-600: #475569;
  --gray-700: #334155;
  --gray-800: #1e293b;
  --gray-900: #0f172a;
  --blue-50: #eff6ff;
  --blue-100: #dbeafe;
  --blue-500: #3b82f6;
  --blue-600: #2563eb;
  --blue-700: #1d4ed8;
  --purple-500: #8b5cf6;
  --purple-600: #7c3aed;
  --green-500: #10b981;
  --orange-500: #f59e0b;
  --shadow-sm: rgba(0, 0, 0, 0.05);
  --shadow-md: rgba(0, 0, 0, 0.1);
  --shadow-lg: rgba(0, 0, 0, 0.15);
  --shadow-xl: rgba(0, 0, 0, 0.25);
}

body {
  background: var(--gray-50);
  color: var(--gray-700);
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.6;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
}

/* Breadcrumb Navigation */
.breadcrumb-nav {
  background: var(--white);
  border-bottom: 1px solid var(--gray-100);
  padding: 1rem 0;
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  list-style: none;
  font-size: 0.875rem;
}

.breadcrumb li {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.breadcrumb li:not(:last-child)::after {
  content: '/';
  color: var(--gray-300);
  margin-left: 0.5rem;
}

.breadcrumb a {
  color: var(--blue-600);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 0.25rem;
  transition: color 0.3s ease;
}

.breadcrumb a:hover {
  color: var(--blue-700);
}

.breadcrumb .active {
  color: var(--gray-600);
  font-weight: 500;
}

/* Hero Section */
.page-hero {
  background: linear-gradient(135deg, var(--blue-600), var(--purple-600));
  color: var(--white);
  padding: 4rem 0;
  position: relative;
  overflow: hidden;
}

.page-hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100"><defs><pattern id="grid" width="10" height="10" patternUnits="userSpaceOnUse"><path d="M 10 0 L 0 0 0 10" fill="none" stroke="rgba(255,255,255,0.1)" stroke-width="0.5"/></pattern></defs><rect width="100" height="100" fill="url(%23grid)"/></svg>');
  z-index: 0;
}

.hero-content {
  position: relative;
  z-index: 1;
  text-align: center;
  max-width: 800px;
  margin: 0 auto;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: rgba(255, 255, 255, 0.2);
  color: var(--white);
  padding: 0.5rem 1rem;
  border-radius: 50px;
  font-size: 0.875rem;
  font-weight: 500;
  margin-bottom: 2rem;
  border: 1px solid rgba(255, 255, 255, 0.3);
}

.hero-title {
  font-size: 3rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
  line-height: 1.1;
}

.subject-name {
  display: block;
  background: linear-gradient(135deg, #ffffff, #e2e8f0);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.exam-name {
  display: block;
  font-size: 0.7em;
  opacity: 0.9;
  margin-top: 0.5rem;
}

.hero-subtitle {
  font-size: 1.25rem;
  opacity: 0.9;
  margin-bottom: 2rem;
  max-width: 600px;
  margin-left: auto;
  margin-right: auto;
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 3rem;
  margin-top: 2rem;
}

.stat-item {
  text-align: center;
}

.stat-number {
  font-size: 2rem;
  font-weight: 700;
  display: block;
}

.stat-label {
  font-size: 0.875rem;
  opacity: 0.8;
  margin-top: 0.25rem;
}

/* Main Content */
.main-content {
  padding: 4rem 0;
}

/* Empty State */
.empty-state {
  text-align: center;
  padding: 4rem 2rem;
  background: var(--white);
  border-radius: 20px;
  box-shadow: 0 4px 16px var(--shadow-sm);
  border: 1px solid var(--gray-100);
}

.empty-icon {
  width: 80px;
  height: 80px;
  background: var(--gray-100);
  border-radius: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 2rem;
}

.empty-icon i {
  font-size: 2rem;
  color: var(--gray-400);
}

.empty-state h2 {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--gray-900);
  margin-bottom: 1rem;
}

.empty-state p {
  color: var(--gray-600);
  margin-bottom: 2rem;
}

/* Section Blocks */
.section-block {
  margin-bottom: 4rem;
  opacity: 0;
  transform: translateY(30px);
  transition: all 0.6s ease;
}

.section-block.animate-in {
  opacity: 1;
  transform: translateY(0);
}

.section-header {
  margin-bottom: 2rem;
}

.section-title {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--gray-900);
  margin-bottom: 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.section-title i {
  color: var(--blue-500);
  font-size: 1.5rem;
}

.section-description {
  color: var(--gray-600);
  font-size: 1rem;
}

/* Papers Grid */
.papers-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(350px, 1fr));
  gap: 2rem;
}

.paper-card {
  background: var(--white);
  border: 2px solid var(--gray-100);
  border-radius: 16px;
  padding: 2rem;
  transition: all 0.3s ease;
  box-shadow: 0 4px 16px var(--shadow-sm);
  opacity: 0;
  transform: translateY(30px);
  position: relative;
  overflow: hidden;
}

.paper-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--blue-500), var(--purple-500));
  transform: scaleX(0);
  transition: transform 0.3s ease;
}

.paper-card:hover::before {
  transform: scaleX(1);
}

.paper-card.animate-in {
  opacity: 1;
  transform: translateY(0);
}

.paper-card:hover {
  transform: translateY(-8px);
  border-color: var(--blue-200);
  box-shadow: 0 20px 40px var(--shadow-lg);
}

.paper-icon {
  width: 60px;
  height: 60px;
  background: linear-gradient(135deg, var(--blue-500), var(--purple-500));
  border-radius: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 1.5rem;
}

.paper-icon i {
  font-size: 1.5rem;
  color: var(--white);
}

.paper-content {
  margin-bottom: 2rem;
}

.paper-title {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--gray-900);
  margin-bottom: 0.5rem;
  line-height: 1.3;
}

.paper-meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  font-size: 0.875rem;
}

.paper-section {
  color: var(--gray-600);
  background: var(--gray-100);
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-weight: 500;
}

.paper-actions {
  display: flex;
  gap: 1rem;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  border-radius: 10px;
  text-decoration: none;
  font-weight: 600;
  font-size: 0.95rem;
  transition: all 0.3s ease;
  border: none;
  cursor: pointer;
}

.btn-primary {
  background: linear-gradient(135deg, var(--blue-600), var(--purple-600));
  color: var(--white);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 24px rgba(59, 130, 246, 0.3);
}

.btn.loading {
  opacity: 0.7;
  cursor: not-allowed;
  transform: none !important;
}

/* Tips Section */
.tips-section {
  background: var(--white);
  padding: 4rem 0;
  border-top: 1px solid var(--gray-100);
}

.tips-header {
  text-align: center;
  margin-bottom: 3rem;
}

.tips-header h2 {
  font-size: 2rem;
  font-weight: 700;
  color: var(--gray-900);
  margin-bottom: 0.5rem;
}

.tips-header p {
  color: var(--gray-600);
  font-size: 1.125rem;
}

.tips-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 2rem;
}

.tip-card {
  background: var(--gray-50);
  padding: 2rem;
  border-radius: 16px;
  text-align: center;
  border: 1px solid var(--gray-100);
  transition: all 0.3s ease;
  opacity: 0;
  transform: translateY(30px);
}

.tip-card.animate-in {
  opacity: 1;
  transform: translateY(0);
}

.tip-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 24px var(--shadow-md);
  background: var(--white);
}

.tip-icon {
  width: 60px;
  height: 60px;
  background: linear-gradient(135deg, var(--orange-500), var(--green-500));
  border-radius: 16px;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 1.5rem;
}

.tip-icon i {
  font-size: 1.5rem;
  color: var(--white);
}

.tip-card h3 {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--gray-900);
  margin-bottom: 0.75rem;
}

.tip-card p {
  color: var(--gray-600);
  line-height: 1.6;
}

/* Responsive Design */
@media (max-width: 768px) {
  .container {
    padding: 0 1rem;
  }

  .page-hero {
    padding: 3rem 0;
  }

  .hero-title {
    font-size: 2.5rem;
  }

  .hero-stats {
    gap: 2rem;
  }

  .stat-number {
    font-size: 1.5rem;
  }

  .main-content {
    padding: 3rem 0;
  }

  .papers-grid {
    grid-template-columns: 1fr;
    gap: 1.5rem;
  }

  .paper-card {
    padding: 1.5rem;
  }

  .section-title {
    font-size: 1.5rem;
  }

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

  .tip-card {
    padding: 1.5rem;
  }
}

@media (max-width: 480px) {
  .page-hero {
    padding: 2rem 0;
  }

  .hero-title {
    font-size: 2rem;
  }

  .hero-subtitle {
    font-size: 1.125rem;
  }

  .hero-stats {
    gap: 1.5rem;
  }

  .breadcrumb {
    font-size: 0.8rem;
  }

  .paper-card {
    padding: 1.25rem;
  }

  .papers-grid {
    gap: 1rem;
  }

  .section-block {
    margin-bottom: 3rem;
  }
}

/* Animation delays for staggered effect */
.paper-card:nth-child(1) { transition-delay: 0.1s; }
.paper-card:nth-child(2) { transition-delay: 0.2s; }
.paper-card:nth-child(3) { transition-delay: 0.3s; }
.paper-card:nth-child(4) { transition-delay: 0.4s; }
.paper-card:nth-child(5) { transition-delay: 0.5s; }
.paper-card:nth-child(6) { transition-delay: 0.6s; }

.tip-card:nth-child(1) { transition-delay: 0.1s; }
.tip-card:nth-child(2) { transition-delay: 0.2s; }
.tip-card:nth-child(3) { transition-delay: 0.3s; }
.tip-card:nth-child(4) { transition-delay: 0.4s; }