/* chemistry.css - NEON BLUE THEME */

/* 🔲 General Cards */
.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 1.5rem;
  margin: 2rem 0;
}

.card {
  border-radius: 14px;
  padding: 1.5rem;
  box-shadow: 0 4px 12px rgba(0,0,0,0.12);
  background: linear-gradient(135deg, #e0f7ff 0%, #ffffff 100%);
  transition: transform 0.3s, box-shadow 0.3s, background 0.3s;
  color: #222;
  border: 1px solid #00ffff; /* Neon blue border */
  cursor: pointer;
}

.card:hover {
  transform: translateY(-6px);
  box-shadow: 0 10px 20px rgba(0,0,0,0.2), 0 0 20px rgba(0, 255, 255, 0.4); /* Neon blue glow */
  background: linear-gradient(135deg, #e0ffff 0%, #ffffff 100%);
}

/* 🌙 Dark Mode Cards */
body.dark .card {
  background: linear-gradient(135deg, #0a1a2a 0%, #050f1a 100%); /* Dark blue gradient */
  color: #f1f1f1;
  box-shadow: 0 4px 12px rgba(255,255,255,0.05);
  border: 1px solid #00ffff; /* Neon blue border */
}

body.dark .card:hover {
  box-shadow: 0 10px 20px rgba(0,0,0,0.3), 0 0 20px rgba(0, 255, 255, 0.5); /* Neon blue glow */
}

/* 🧪 Main Content */
.content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem;
}

.content h1 {
  text-align: center;
  color: #00ffff; /* Neon blue */
  text-shadow: 0 0 10px rgba(0, 255, 255, 0.5); /* Neon blue glow */
  margin-bottom: 1rem;
}

.content h2 {
  color: #00bfff; /* Bright blue */
  border-bottom: 2px solid #00ffff; /* Neon blue */
  padding-bottom: 0.5rem;
  margin: 2rem 0 1rem 0;
}

/* ================================
   CHAPTER STYLES - NEON BLUE THEME
================================ */
.chapter-container {
  background: linear-gradient(135deg, rgba(10, 25, 47, 0.9), rgba(5, 15, 30, 0.9)); /* Dark blue gradient */
  border: 1px solid rgba(0, 255, 255, 0.4); /* Neon blue border */
  border-radius: 15px;
  margin: 2rem 0;
  padding: 0;
  overflow: hidden;
  backdrop-filter: blur(10px);
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
  transition: all 0.3s ease;
}

.chapter-container:hover {
  border-color: rgba(0, 255, 255, 0.8); /* Brighter neon blue */
  box-shadow: 0 12px 40px rgba(0, 255, 255, 0.3); /* Neon blue glow */
}

.chapter-header {
  background: linear-gradient(135deg, rgba(0, 255, 255, 0.15), rgba(0, 191, 255, 0.1)); /* Neon blue to blue gradient */
  padding: 1.5rem 2rem;
  border-bottom: 1px solid rgba(0, 255, 255, 0.3); /* Neon blue border */
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
  transition: all 0.3s ease;
}

.chapter-header:hover {
  background: linear-gradient(135deg, rgba(0, 255, 255, 0.2), rgba(0, 191, 255, 0.15)); /* Brighter blue gradient */
}

.chapter-header h3 {
  color: #00ffff; /* Neon blue */
  margin: 0;
  font-size: 1.4rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 10px;
}

.chapter-header h3::before {
  content: "🧪";
  font-size: 1.2rem;
}

.toggle-btn {
  background: linear-gradient(45deg, #00ffff, #0099ff); /* Neon blue to blue gradient */
  border: none;
  color: #0a0a1a;
  padding: 0.5rem 1rem;
  border-radius: 8px;
  cursor: pointer;
  font-weight: bold;
  transition: all 0.3s ease;
  display: flex;
  align-items: center;
  gap: 5px;
}

.toggle-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 15px rgba(0, 255, 255, 0.5); /* Neon blue glow */
}

/* FIXED CHAPTER STYLES */
.chapter-content {
  padding: 0;
  display: none !important;  /* FORCE hide initially */
}

.chapter-content.active {
  display: block !important;  /* FORCE show when active */
}

.notes-section {
  padding: 2rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
}

.notes-content {
  line-height: 1.8;
  color: #e0e0ff;
  font-size: 1.1rem;
}

.notes-content h1, .notes-content h2, .notes-content h3, .notes-content h4 {
  color: #00ffff; /* Neon blue */
  margin: 1.5rem 0 1rem 0;
}

.notes-content p {
  margin-bottom: 1rem;
}

.notes-content ul, .notes-content ol {
  margin: 1rem 0;
  padding-left: 2rem;
}

.notes-content li {
  margin-bottom: 0.5rem;
}

.notes-content code {
  background: rgba(0, 255, 255, 0.1); /* Neon blue background */
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
  color: #00ffff; /* Neon blue text */
  font-family: 'Courier New', monospace;
}

.chemical-formula {
  background: rgba(0, 191, 255, 0.1); /* Blue background */
  padding: 1rem;
  border-radius: 8px;
  border-left: 4px solid #00bfff; /* Bright blue */
  margin: 1rem 0;
  font-family: 'Courier New', monospace;
  font-size: 1.1rem;
}

.file-download-section {
  padding: 2rem;
  background: rgba(0, 255, 255, 0.05); /* Neon blue tint */
  border-top: 1px solid rgba(0, 255, 255, 0.2); /* Neon blue border */
}

.file-info {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1rem;
  padding: 1rem;
  background: rgba(255, 255, 255, 0.05);
  border-radius: 10px;
  border-left: 4px solid #00ffff; /* Neon blue */
}

.file-icon {
  font-size: 2rem;
  color: #00ffff; /* Neon blue */
}

.file-details h4 {
  color: #00ffff; /* Neon blue */
  margin: 0 0 0.5rem 0;
  font-size: 1.1rem;
}

.file-meta {
  color: #a0a0c0;
  font-size: 0.9rem;
}

.download-btn {
  background: linear-gradient(45deg, #0099ff, #00ffff); /* Blue to neon blue */
  color: #0a0a1a;
  border: none;
  padding: 0.75rem 1.5rem;
  border-radius: 8px;
  text-decoration: none;
  font-weight: bold;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  transition: all 0.3s ease;
  cursor: pointer;
}

.download-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(0, 255, 255, 0.4); /* Neon blue glow */
}

.no-file-notice {
  text-align: center;
  padding: 1.5rem;
  color: #a0a0c0;
  background: rgba(255, 255, 255, 0.05);
  border-radius: 10px;
  border: 1px dashed rgba(255, 255, 255, 0.2);
}

.questions-section {
  padding: 2rem;
  background: rgba(0, 191, 255, 0.05); /* Blue tint */
}

.questions-section h4 {
  color: #00bfff; /* Bright blue */
  margin-bottom: 1rem;
  font-size: 1.2rem;
  display: flex;
  align-items: center;
  gap: 8px;
}

.questions-section h4::before {
  content: "🔬";
}

.questions-section ul {
  list-style: none;
  padding: 0;
}

.questions-section li {
  background: rgba(255, 255, 255, 0.05);
  margin: 0.5rem 0;
  padding: 1rem;
  border-radius: 8px;
  border-left: 3px solid #00bfff; /* Bright blue */
  transition: all 0.3s ease;
}

.questions-section li:hover {
  background: rgba(255, 255, 255, 0.1);
  transform: translateX(5px);
}

/* Chemistry-specific elements */
.periodic-table-preview {
  background: rgba(0, 191, 255, 0.1); /* Blue background */
  padding: 1.5rem;
  border-radius: 10px;
  margin: 1rem 0;
  border: 1px solid rgba(0, 191, 255, 0.3); /* Blue border */
}

.element-card {
  display: inline-block;
  width: 60px;
  height: 60px;
  background: linear-gradient(45deg, #00ffff, #0099ff); /* Neon blue to blue */
  color: #0a0a1a;
  text-align: center;
  line-height: 60px;
  margin: 5px;
  border-radius: 8px;
  font-weight: bold;
  font-size: 0.8rem;
  cursor: pointer;
  transition: all 0.3s ease;
}

.element-card:hover {
  transform: scale(1.1);
  box-shadow: 0 4px 15px rgba(0, 255, 255, 0.4); /* Neon blue glow */
}

/* 🧠 Flashcards */
.flashcards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
  margin: 2rem 0;
}

.flashcard {
  perspective: 1000px;
  cursor: pointer;
  height: 140px;
  position: relative;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  transition: transform 0.6s;
  transform-style: preserve-3d;
}

.flashcard.flipped .flashcard-inner {
  transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
  position: absolute;
  width: 100%;
  height: 100%;
  border-radius: 12px;
  backface-visibility: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: bold;
  padding: 1rem;
  text-align: center;
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.flashcard-front {
  background: linear-gradient(135deg, #00ffff, #0099ff); /* Neon blue to blue */
  color: #fff;
}

.flashcard-back {
  background: #e6ffff; /* Light blue */
  color: #222;
  transform: rotateY(180deg);
}

/* Dark mode flashcards */
body.dark .flashcard-front {
  background: linear-gradient(135deg, #00ffff, #0088cc);
}

body.dark .flashcard-back {
  background: #333;
  color: #eee;
}

/* ⚖️ Equation Balancer */
.balancer {
  background: rgba(255, 255, 255, 0.1);
  padding: 1.5rem;
  border-radius: 12px;
  margin: 2rem 0;
  text-align: center;
}

#chemicalEquation {
  width: 300px;
  max-width: 100%;
  padding: 0.8rem;
  border: 2px solid #00ffff; /* Neon blue */
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.1);
  color: inherit;
  font-size: 1rem;
  margin-right: 1rem;
}

.balancer button {
  background: linear-gradient(135deg, #00ffff, #0099ff); /* Neon blue to blue */
  color: white;
  border: none;
  padding: 0.8rem 1.5rem;
  border-radius: 8px;
  cursor: pointer;
  font-size: 1rem;
  transition: all 0.3s ease;
}

.balancer button:hover {
  transform: scale(1.05);
  box-shadow: 0 0 15px rgba(0, 255, 255, 0.5); /* Neon blue glow */
}

#balancedResult {
  margin-top: 1rem;
  font-weight: bold;
  min-height: 1.5rem;
  color: #00ffff; /* Neon blue */
}

/* 🔍 Element Search */
#elementSearch {
  width: 200px;
  padding: 0.8rem;
  border: 2px solid #00bfff; /* Bright blue */
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.1);
  color: inherit;
  font-size: 1rem;
  margin: 1rem 0;
}

#elementInfo {
  background: rgba(255, 255, 255, 0.1);
  padding: 1rem;
  border-radius: 8px;
  margin: 1rem 0;
  border-left: 4px solid #00ffff; /* Neon blue */
}

/* 🧮 Molar Mass Calculator */
.calculator {
  background: rgba(255, 255, 255, 0.1);
  padding: 1.5rem;
  border-radius: 12px;
  margin: 2rem 0;
  text-align: center;
}

#compoundInput {
  width: 200px;
  padding: 0.8rem;
  border: 2px solid #00bfff; /* Bright blue */
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.1);
  color: inherit;
  font-size: 1rem;
  margin-right: 1rem;
}

.calculator button {
  background: linear-gradient(135deg, #00ffff, #0099ff); /* Neon blue to blue */
  color: white;
  border: none;
  padding: 0.8rem 1.5rem;
  border-radius: 8px;
  cursor: pointer;
  font-size: 1rem;
  transition: all 0.3s ease;
}

.calculator button:hover {
  transform: scale(1.05);
  box-shadow: 0 0 15px rgba(0, 255, 255, 0.5); /* Neon blue glow */
}

#molarMassResult {
  margin-top: 1rem;
  font-weight: bold;
  min-height: 1.5rem;
  color: #00bfff; /* Bright blue */
}

/* 📝 Quiz Sections */
.quiz {
  background: rgba(255, 255, 255, 0.1);
  padding: 1rem;
  border-radius: 8px;
  margin: 1rem 0;
  border-left: 4px solid #00bfff; /* Bright blue */
}

.quiz button {
  background: #00bfff; /* Bright blue */
  color: #0a0a1a;
  border: none;
  padding: 0.5rem 1rem;
  border-radius: 6px;
  cursor: pointer;
  margin-top: 0.5rem;
  font-weight: bold;
}

.quiz button:hover {
  background: #33ccff; /* Lighter blue */
}

/* ⚠️ Common Mistakes */
.content ul {
  background: rgba(255, 255, 255, 0.1);
  padding: 1.5rem;
  border-radius: 12px;
  border-left: 4px solid #ff4444;
}

/* 🔗 CTA Button */
.cta {
  background: linear-gradient(135deg, #00ffff, #0099ff); /* Neon blue to blue */
  color: white;
  border: none;
  padding: 1rem 2rem;
  border-radius: 10px;
  cursor: pointer;
  font-size: 1.1rem;
  font-weight: bold;
  transition: all 0.3s ease;
  display: block;
  margin: 2rem auto;
  text-align: center;
  width: fit-content;
}

.cta:hover {
  transform: scale(1.05);
  box-shadow: 0 0 20px rgba(0, 255, 255, 0.5), 0 0 40px rgba(0, 153, 255, 0.3); /* Neon blue glow */
}

/* Chemistry Hero */
.chemistry-hero {
  text-align: center;
  padding: 4rem 2rem;
  position: relative;
}

.chemistry-hero h1 {
  background: linear-gradient(135deg, #00ffff, #0099ff); /* Neon blue to blue */
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  font-size: 4rem;
  font-weight: 800;
  line-height: 1.1;
  margin-bottom: 1rem;
}

.typewriter {
  text-align: center;
  font-size: 1.4rem;
  color: #666;
  margin: 0 auto 2rem auto;
  max-width: 800px;
  overflow: hidden;
  border-right: 2px solid #00ffff; /* Neon blue */
  white-space: nowrap;
  animation: typing 4s steps(50, end), blink-caret 0.75s step-end infinite;
}

@keyframes typing {
  from { width: 0 }
  to { width: 100% }
}

@keyframes blink-caret {
  from, to { border-color: transparent }
  50% { border-color: #00ffff; } /* Neon blue */
}

/* Dark mode */
body.dark .typewriter {
  color: #ccc;
}

/* PDF Download Section */
.pdf-download-section {
  background: linear-gradient(135deg, #00ffff 0%, #0099ff 100%); /* Neon blue to blue */
  color: white;
  padding: 25px;
  border-radius: 12px;
  margin: 25px 0;
  text-align: center;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

.pdf-header h3 {
  font-size: 1.5rem;
  margin-bottom: 10px;
}

.pdf-header p {
  opacity: 0.9;
  margin-bottom: 20px;
}

.pdf-features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 15px;
  margin: 20px 0;
}

.feature {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  padding: 10px;
  background: rgba(255, 255, 255, 0.1);
  border-radius: 8px;
}

.feature .icon {
  font-size: 1.5rem;
}

.download-btn {
  background: #00ffff; /* Neon blue */
  color: white;
  border: none;
  padding: 12px 30px;
  font-size: 1.1rem;
  border-radius: 50px;
  cursor: pointer;
  transition: all 0.3s ease;
  display: inline-flex;
  align-items: center;
  gap: 10px;
  margin: 15px 0;
  box-shadow: 0 4px 10px rgba(0, 255, 255, 0.3); /* Neon blue glow */
}

.download-btn:hover {
  background: #00e6e6; /* Slightly darker neon blue */
  transform: translateY(-2px);
  box-shadow: 0 6px 15px rgba(0, 255, 255, 0.4); /* Neon blue glow */
}

.download-note {
  font-size: 0.9rem;
  opacity: 0.8;
  margin-top: 10px;
}

/* Animation for content reveal */
@keyframes slideDown {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.chapter-content.active {
  animation: slideDown 0.3s ease-out;
}

/* Responsive Design */
@media (max-width: 768px) {
  .content {
    padding: 1rem;
  }
  
  .cards {
    grid-template-columns: 1fr;
  }
  
  .chapter-header {
    padding: 1rem;
    flex-direction: column;
    gap: 1rem;
    align-items: flex-start;
  }

  .chapter-header h3 {
    font-size: 1.2rem;
  }

  .notes-section,
  .file-download-section,
  .questions-section {
    padding: 1.5rem;
  }

  .file-info {
    flex-direction: column;
    text-align: center;
    gap: 0.5rem;
  }

  .element-card {
    width: 50px;
    height: 50px;
    line-height: 50px;
    font-size: 0.7rem;
  }
  
  .flashcards {
    grid-template-columns: 1fr;
  }
  
  #chemicalEquation,
  #compoundInput {
    width: 100%;
    margin: 0 0 1rem 0;
  }
  
  .balancer button,
  .calculator button {
    width: 100%;
  }
  
  .chemistry-hero h1 {
    font-size: 2.5rem;
  }
  
  .pdf-features {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 480px) {
  .chemistry-hero h1 {
    font-size: 2rem;
  }
  
  .typewriter {
    font-size: 1.1rem;
  }
}

   /* Enhanced Chapter Styles for Chemistry - NEON BLUE THEME */
    .chapter-container {
      background: linear-gradient(135deg, rgba(10, 25, 47, 0.9), rgba(5, 15, 30, 0.9));
      border: 1px solid rgba(0, 255, 255, 0.4);
      border-radius: 15px;
      margin: 2rem 0;
      padding: 0;
      overflow: hidden;
      backdrop-filter: blur(10px);
      box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
      transition: all 0.3s ease;
    }

    .chapter-container:hover {
      border-color: rgba(0, 255, 255, 0.8);
      box-shadow: 0 12px 40px rgba(0, 255, 255, 0.3);
    }

    .chapter-header {
      background: linear-gradient(135deg, rgba(0, 255, 255, 0.15), rgba(0, 191, 255, 0.1));
      padding: 1.5rem 2rem;
      border-bottom: 1px solid rgba(0, 255, 255, 0.3);
      display: flex;
      justify-content: space-between;
      align-items: center;
      cursor: pointer;
      transition: all 0.3s ease;
    }

    .chapter-header:hover {
      background: linear-gradient(135deg, rgba(0, 255, 255, 0.2), rgba(0, 191, 255, 0.15));
    }

    .chapter-header h3 {
      color: #00ffff;
      margin: 0;
      font-size: 1.4rem;
      font-weight: 600;
      display: flex;
      align-items: center;
      gap: 10px;
    }

    .chapter-header h3::before {
      content: "🧪";
      font-size: 1.2rem;
    }

    .toggle-btn {
      background: linear-gradient(45deg, #00ffff, #0099ff);
      border: none;
      color: #0a0a1a;
      padding: 0.5rem 1rem;
      border-radius: 8px;
      cursor: pointer;
      font-weight: bold;
      transition: all 0.3s ease;
      display: flex;
      align-items: center;
      gap: 5px;
    }

    .toggle-btn:hover {
      transform: translateY(-2px);
      box-shadow: 0 4px 15px rgba(0, 255, 255, 0.5);
    }

    .chapter-content {
      padding: 0;
      display: none;
    }

    .chapter-content.active {
      display: block;
    }

    .notes-section {
      padding: 2rem;
      border-bottom: 1px solid rgba(255, 255, 255, 0.1);
    }

    .notes-content {
      line-height: 1.8;
      color: #e0e0ff;
      font-size: 1.1rem;
    }

    .notes-content h1, .notes-content h2, .notes-content h3, .notes-content h4 {
      color: #00ffff;
      margin: 1.5rem 0 1rem 0;
    }

    .notes-content p {
      margin-bottom: 1rem;
    }

    .notes-content ul, .notes-content ol {
      margin: 1rem 0;
      padding-left: 2rem;
    }

    .notes-content li {
      margin-bottom: 0.5rem;
    }

    .notes-content code {
      background: rgba(0, 255, 255, 0.1);
      padding: 0.2rem 0.5rem;
      border-radius: 4px;
      color: #00ffff;
      font-family: 'Courier New', monospace;
    }

    .chemical-formula {
      background: rgba(0, 191, 255, 0.1);
      padding: 1rem;
      border-radius: 8px;
      border-left: 4px solid #00bfff;
      margin: 1rem 0;
      font-family: 'Courier New', monospace;
      font-size: 1.1rem;
    }

    .file-download-section {
      padding: 2rem;
      background: rgba(0, 255, 255, 0.05);
      border-top: 1px solid rgba(0, 255, 255, 0.2);
    }

    .file-info {
      display: flex;
      align-items: center;
      gap: 1rem;
      margin-bottom: 1rem;
      padding: 1rem;
      background: rgba(255, 255, 255, 0.05);
      border-radius: 10px;
      border-left: 4px solid #00ffff;
    }

    .file-icon {
      font-size: 2rem;
      color: #00ffff;
    }

    .file-details h4 {
      color: #00ffff;
      margin: 0 0 0.5rem 0;
      font-size: 1.1rem;
    }

    .file-meta {
      color: #a0a0c0;
      font-size: 0.9rem;
    }

    .download-btn {
      background: linear-gradient(45deg, #0099ff, #00ffff);
      color: #0a0a1a;
      border: none;
      padding: 0.75rem 1.5rem;
      border-radius: 8px;
      text-decoration: none;
      font-weight: bold;
      display: inline-flex;
      align-items: center;
      gap: 8px;
      transition: all 0.3s ease;
      cursor: pointer;
    }

    .download-btn:hover {
      transform: translateY(-2px);
      box-shadow: 0 6px 20px rgba(0, 255, 255, 0.4);
    }

    .no-file-notice {
      text-align: center;
      padding: 1.5rem;
      color: #a0a0c0;
      background: rgba(255, 255, 255, 0.05);
      border-radius: 10px;
      border: 1px dashed rgba(255, 255, 255, 0.2);
    }

    .questions-section {
      padding: 2rem;
      background: rgba(0, 191, 255, 0.05);
    }

    .questions-section h4 {
      color: #00bfff;
      margin-bottom: 1rem;
      font-size: 1.2rem;
      display: flex;
      align-items: center;
      gap: 8px;
    }

    .questions-section h4::before {
      content: "🔬";
    }

    .questions-section ul {
      list-style: none;
      padding: 0;
    }

    .questions-section li {
      background: rgba(255, 255, 255, 0.05);
      margin: 0.5rem 0;
      padding: 1rem;
      border-radius: 8px;
      border-left: 3px solid #00bfff;
      transition: all 0.3s ease;
    }

    .questions-section li:hover {
      background: rgba(255, 255, 255, 0.1);
      transform: translateX(5px);
    }

    /* Chemistry-specific elements */
    .periodic-table-preview {
      background: rgba(0, 191, 255, 0.1);
      padding: 1.5rem;
      border-radius: 10px;
      margin: 1rem 0;
      border: 1px solid rgba(0, 191, 255, 0.3);
    }

    .element-card {
      display: inline-block;
      width: 60px;
      height: 60px;
      background: linear-gradient(45deg, #00ffff, #0099ff);
      color: #0a0a1a;
      text-align: center;
      line-height: 60px;
      margin: 5px;
      border-radius: 8px;
      font-weight: bold;
      font-size: 0.8rem;
      cursor: pointer;
      transition: all 0.3s ease;
    }

    .element-card:hover {
      transform: scale(1.1);
      box-shadow: 0 4px 15px rgba(0, 255, 255, 0.4);
    }

    /* Responsive Design */
    @media (max-width: 768px) {
      .chapter-header {
        padding: 1rem;
        flex-direction: column;
        gap: 1rem;
        align-items: flex-start;
      }

      .chapter-header h3 {
        font-size: 1.2rem;
      }

      .notes-section,
      .file-download-section,
      .questions-section {
        padding: 1.5rem;
      }

      .file-info {
        flex-direction: column;
        text-align: center;
        gap: 0.5rem;
      }

      .element-card {
        width: 50px;
        height: 50px;
        line-height: 50px;
        font-size: 0.7rem;
      }
    }

    /* Animation for content reveal */
    @keyframes slideDown {
      from {
        opacity: 0;
        transform: translateY(-10px);
      }
      to {
        opacity: 1;
        transform: translateY(0);
      }
    }

    .chapter-content.active {
      animation: slideDown 0.3s ease-out;
    }