@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

/* Minimalist Design Tokens */
:root {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --card-bg: #ffffff;
  --card-border: #e2e8f0;
  --card-hover-border: #cbd5e1;
  --primary: #0f172a; /* Dark slate */
  --accent: #2563eb;  /* Clean classic blue */
  --accent-hover: #1d4ed8;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --font-family: 'Inter', sans-serif;
  --transition: all 0.2s ease-in-out;
}

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.5;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Layout Container */
.container {
  width: 100%;
  max-width: 1000px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Navigation Header */
header {
  background-color: var(--bg-secondary);
  border-bottom: 1px solid var(--card-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-wrapper {
  display: flex;
  justify-content: space-between;
  align-items: center;
  height: 64px;
}

.logo {
  display: flex;
  align-items: center;
  gap: 8px;
  text-decoration: none;
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--text-primary);
}

.logo-icon {
  width: 24px;
  height: 24px;
  background-color: var(--primary);
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
}

.logo-icon::before {
  content: "AI";
  color: #ffffff;
  font-weight: 800;
  font-size: 0.7rem;
}

.nav-links {
  display: flex;
  gap: 12px;
}

.nav-btn {
  text-decoration: none;
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 0.9rem;
  padding: 8px 14px;
  border-radius: 6px;
  transition: var(--transition);
}

.nav-btn:hover, .nav-btn.active {
  color: var(--text-primary);
  background-color: #f1f5f9;
}

.btn-home {
  font-size: 0.85rem;
  border: 1px solid var(--card-border);
}

/* Hero Section */
.hero {
  padding: 60px 0 40px 0;
  text-align: center;
}

.hero h1 {
  font-size: 2.2rem;
  font-weight: 800;
  line-height: 1.25;
  color: var(--text-primary);
  margin-bottom: 12px;
  letter-spacing: -0.5px;
}

.hero p {
  color: var(--text-secondary);
  font-size: 1.05rem;
  max-width: 650px;
  margin: 0 auto 20px auto;
}

.institution {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.inst-tag {
  font-size: 0.8rem;
  color: var(--text-muted);
  background-color: #f1f5f9;
  padding: 4px 10px;
  border-radius: 4px;
  border: 1px solid var(--card-border);
}

/* Categories Grid */
.categories {
  padding: 20px 0 60px 0;
}

.section-title {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 24px;
  text-align: center;
  color: var(--text-primary);
}

.category-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 20px;
}

.cat-card {
  background-color: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 8px;
  padding: 24px;
  text-decoration: none;
  color: inherit;
  transition: var(--transition);
  display: flex;
  flex-direction: column;
}

.cat-card:hover {
  border-color: var(--card-hover-border);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.03);
}

.cat-icon {
  font-size: 1.4rem;
  margin-bottom: 12px;
}

.cat-card h3 {
  font-size: 1.1rem;
  font-weight: 600;
  margin-bottom: 8px;
  color: var(--text-primary);
}

.cat-card p {
  color: var(--text-secondary);
  font-size: 0.9rem;
  line-height: 1.4;
  margin-bottom: 16px;
}

.cat-link {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--accent);
  margin-top: auto;
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.cat-card:hover .cat-link {
  color: var(--accent-hover);
}

.coming-soon-badge {
  background-color: #f1f5f9;
  border: 1px solid var(--card-border);
  color: var(--text-muted);
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 0.7rem;
  font-weight: 600;
}

/* Tabs layout for subpages */
.tabs-container {
  display: flex;
  flex-direction: column;
  gap: 30px;
  margin-top: 10px;
  margin-bottom: 60px;
}

/* Hide Radio Inputs */
.tabs-container input[type="radio"] {
  display: none;
}

/* Scrollable Tabs Nav */
.tabs-nav {
  display: flex;
  gap: 6px;
  overflow-x: auto;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--card-border);
}

.tabs-nav label {
  padding: 8px 16px;
  background-color: #f1f5f9;
  border: 1px solid var(--card-border);
  border-radius: 20px;
  color: var(--text-secondary);
  cursor: pointer;
  font-weight: 500;
  font-size: 0.85rem;
  transition: var(--transition);
  white-space: nowrap;
  user-select: none;
}

.tabs-nav label:hover {
  background-color: #e2e8f0;
  color: var(--text-primary);
}

/* Content Area */
.tabs-content {
  position: relative;
}

.tab-pane {
  display: none;
  grid-template-columns: repeat(2, 1fr);
  gap: 16px;
}

/* Show Content based on Checked Radio Button */
#sem1:checked ~ .tabs-content .pane-sem1,
#sem2:checked ~ .tabs-content .pane-sem2,
#sem3:checked ~ .tabs-content .pane-sem3,
#sem4:checked ~ .tabs-content .pane-sem4,
#sem5:checked ~ .tabs-content .pane-sem5,
#sem6:checked ~ .tabs-content .pane-sem6,
#sem7:checked ~ .tabs-content .pane-sem7,
#sem8:checked ~ .tabs-content .pane-sem8 {
  display: grid;
}

/* Active Label Style */
#sem1:checked ~ .tabs-nav label[for="sem1"],
#sem2:checked ~ .tabs-nav label[for="sem2"],
#sem3:checked ~ .tabs-nav label[for="sem3"],
#sem4:checked ~ .tabs-nav label[for="sem4"],
#sem5:checked ~ .tabs-nav label[for="sem5"],
#sem6:checked ~ .tabs-nav label[for="sem6"],
#sem7:checked ~ .tabs-nav label[for="sem7"],
#sem8:checked ~ .tabs-nav label[for="sem8"] {
  background-color: var(--primary);
  border-color: var(--primary);
  color: #ffffff;
}

/* Subject Card Styles */
.subject-card {
  background-color: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 8px;
  padding: 20px;
  display: flex;
  flex-direction: column;
}

.subject-code {
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--text-muted);
  margin-bottom: 4px;
}

.subject-card h3 {
  font-size: 1rem;
  font-weight: 600;
  margin-bottom: 14px;
  color: var(--text-primary);
}

.card-meta {
  margin-top: auto;
}

.download-link, .syllabus-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  color: var(--text-secondary);
  background-color: #f1f5f9;
  border: 1px solid var(--card-border);
  padding: 8px 12px;
  border-radius: 6px;
  font-size: 0.8rem;
  font-weight: 600;
  transition: var(--transition);
  width: 100%;
}

.download-link:hover, .syllabus-link:hover {
  background-color: var(--primary);
  border-color: var(--primary);
  color: #ffffff;
}

/* Coming Soon Screen */
.coming-soon-wrapper {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  padding: 80px 20px;
}

.cs-icon {
  font-size: 2.5rem;
  margin-bottom: 16px;
}

.coming-soon-wrapper h1 {
  font-size: 2rem;
  font-weight: 800;
  margin-bottom: 8px;
  color: var(--text-primary);
}

.coming-soon-wrapper p {
  color: var(--text-secondary);
  font-size: 0.95rem;
  max-width: 450px;
  margin-bottom: 24px;
}

.btn-primary {
  display: inline-flex;
  align-items: center;
  text-decoration: none;
  color: #ffffff;
  background-color: var(--primary);
  padding: 10px 20px;
  border-radius: 6px;
  font-weight: 600;
  font-size: 0.9rem;
  transition: var(--transition);
}

.btn-primary:hover {
  background-color: #334155;
}

/* Footer Section */
footer {
  margin-top: auto;
  border-top: 1px solid var(--card-border);
  padding: 24px 0;
  background-color: var(--bg-secondary);
}

.footer-wrapper {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 12px;
}

.footer-info {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.footer-credit {
  font-size: 0.8rem;
  color: var(--text-secondary);
  font-weight: 500;
}

/* Responsiveness */
@media (max-width: 768px) {
  .category-grid, .tab-pane {
    grid-template-columns: 1fr;
  }
  
  .nav-wrapper {
    flex-direction: column;
    height: auto;
    padding: 12px 0;
    gap: 8px;
  }
  
  .hero h1 {
    font-size: 1.8rem;
  }
  
  .footer-wrapper {
    flex-direction: column;
    text-align: center;
  }
}