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

:root {
  --primary: #0066cc;
  --primary-dark: #0052a3;
  --primary-light: #e6f0ff;
  --secondary: #64748b;
  --success: #10b981;
  --warning: #f59e0b;
  --danger: #ef4444;
  --bg: #f8fafc;
  --card-bg: #ffffff;
  --text: #1e293b;
  --text-muted: #64748b;
  --border: #e2e8f0;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 40px rgba(0, 0, 0, 0.12);
  --radius: 12px;
  --radius-sm: 8px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
}

.app {
  display: flex;
  min-height: 100vh;
}

/* Sidebar */
.sidebar {
  width: 280px;
  background: var(--card-bg);
  border-right: 1px solid var(--border);
  padding: 24px 16px;
  display: flex;
  flex-direction: column;
  position: fixed;
  height: 100vh;
  overflow-y: auto;
  z-index: 100;
  transition: transform 0.3s;
}

.sidebar-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 32px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border);
}

.logo {
  display: flex;
  align-items: center;
  gap: 12px;
}

.logo-icon {
  font-size: 28px;
}

.logo-text {
  font-size: 16px;
  font-weight: 600;
  color: var(--text);
}

.close-sidebar {
  display: none;
}

.nav {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  text-decoration: none;
  transition: all 0.2s;
  cursor: pointer;
}

.nav-item:hover {
  background: var(--bg);
  color: var(--text);
}

.nav-item.active {
  background: var(--primary-light);
  color: var(--primary);
  font-weight: 500;
}

.nav-icon {
  font-size: 20px;
  width: 24px;
  text-align: center;
}

.sidebar-footer {
  margin-top: auto;
  padding-top: 16px;
  border-top: 1px solid var(--border);
}

/* Main Content */
.main-content {
  flex: 1;
  margin-left: 280px;
  padding: 32px;
  min-height: 100vh;
}

.mobile-header {
  display: none;
  align-items: center;
  gap: 16px;
  padding: 16px 24px;
  background: var(--card-bg);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 50;
}

.mobile-title {
  font-size: 18px;
  font-weight: 600;
}

/* Pages */
.page {
  display: none;
  animation: fadeIn 0.3s;
}

.page.active {
  display: block;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

.page-title {
  font-size: 28px;
  font-weight: 600;
  margin-bottom: 32px;
  color: var(--text);
}

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

.hero-title {
  font-size: 36px;
  font-weight: 700;
  margin-bottom: 32px;
  color: var(--text);
}

.search-box {
  max-width: 600px;
  margin: 0 auto 24px;
  display: flex;
  gap: 12px;
}

.search-input {
  flex: 1;
  padding: 14px 20px;
  font-size: 16px;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  background: var(--card-bg);
  transition: border-color 0.2s, box-shadow 0.2s;
}

.search-input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 4px rgba(0, 102, 204, 0.1);
}

.search-input.large {
  max-width: 600px;
  margin: 0 auto;
}

.quick-questions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 8px;
  align-items: center;
}

.qq-label {
  color: var(--text-muted);
  font-size: 14px;
}

.qq-btn {
  padding: 8px 16px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 20px;
  font-size: 14px;
  color: var(--text-muted);
  cursor: pointer;
  transition: all 0.2s;
}

.qq-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
  background: var(--primary-light);
}

/* Upload Section */
.upload-section {
  max-width: 600px;
  margin: 40px auto;
}

.upload-card {
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  border-radius: var(--radius);
  padding: 40px;
  text-align: center;
  color: white;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
  border: 2px dashed rgba(255, 255, 255, 0.3);
}

.upload-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.upload-card.dragover {
  border-color: white;
  background: rgba(255, 255, 255, 0.1);
}

.upload-icon {
  font-size: 48px;
  margin-bottom: 16px;
}

.upload-card h3 {
  font-size: 20px;
  margin-bottom: 8px;
}

.upload-card p {
  opacity: 0.9;
  margin-bottom: 20px;
  font-size: 14px;
}

/* Quick Solutions */
.quick-solutions {
  margin-top: 60px;
}

.section-title {
  font-size: 22px;
  font-weight: 600;
  margin-bottom: 24px;
  text-align: center;
}

.solutions-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 16px;
  max-width: 900px;
  margin: 0 auto;
}

.solution-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 24px 16px;
  text-align: center;
  cursor: pointer;
  transition: all 0.2s;
  box-shadow: var(--shadow);
}

.solution-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.solution-icon {
  font-size: 32px;
  margin-bottom: 12px;
}

.solution-card h3 {
  font-size: 14px;
  font-weight: 500;
  color: var(--text);
}

/* Features Grid */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 24px;
  margin-top: 60px;
  max-width: 1000px;
  margin-left: auto;
  margin-right: auto;
}

.feature-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 32px 24px;
  text-align: center;
  cursor: pointer;
  transition: all 0.2s;
  box-shadow: var(--shadow);
}

.feature-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
}

.feature-icon {
  font-size: 40px;
  margin-bottom: 16px;
}

.feature-card h3 {
  font-size: 18px;
  margin-bottom: 8px;
}

.feature-card p {
  color: var(--text-muted);
  font-size: 14px;
}

/* Buttons */
.btn {
  padding: 12px 24px;
  font-size: 15px;
  font-weight: 500;
  border: none;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  justify-content: center;
}

.btn:active {
  transform: scale(0.98);
}

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

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

.btn-secondary {
  background: var(--card-bg);
  color: var(--text);
  border: 1px solid var(--border);
}

.btn-secondary:hover {
  background: var(--bg);
}

.btn-large {
  padding: 14px 32px;
  font-size: 16px;
  width: 100%;
}

.btn-icon {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: none;
  background: transparent;
  cursor: pointer;
  font-size: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.2s;
  color: var(--text-muted);
}

.btn-icon:hover {
  background: var(--bg);
}

.btn-close {
  width: 32px;
  height: 32px;
  border-radius: 6px;
  border: none;
  background: transparent;
  cursor: pointer;
  font-size: 24px;
  color: var(--text-muted);
  transition: background 0.2s;
  display: flex;
  align-items: center;
  justify-content: center;
}

.btn-close:hover {
  background: var(--bg);
}

/* Cards */
.card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  margin-bottom: 24px;
}

/* Search Section */
.search-section {
  max-width: 700px;
  margin: 0 auto 40px;
  text-align: center;
}

.search-section .search-input {
  width: 100%;
  margin-bottom: 16px;
}

/* Lessons List */
.lessons-list,
.instructions-list,
.faq-list {
  max-width: 800px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.lesson-card,
.instruction-card,
.faq-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  cursor: pointer;
  transition: all 0.2s;
}

.lesson-card:hover,
.instruction-card:hover,
.faq-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.lesson-header,
.instruction-header {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 12px;
}

.lesson-icon,
.instruction-icon {
  font-size: 32px;
  width: 56px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--primary-light);
  border-radius: var(--radius-sm);
}

.lesson-title,
.instruction-title {
  font-size: 18px;
  font-weight: 600;
}

.lesson-desc,
.instruction-desc {
  color: var(--text-muted);
  font-size: 14px;
}

.faq-card {
  padding: 20px 24px;
}

.faq-question {
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
  font-weight: 500;
}

.faq-icon {
  font-size: 20px;
  transition: transform 0.3s;
}

.faq-card.active .faq-icon {
  transform: rotate(45deg);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s;
  padding-top: 0;
  color: var(--text-muted);
  line-height: 1.7;
}

.faq-card.active .faq-answer {
  max-height: 500px;
  padding-top: 16px;
}

/* Errors Grid */
.errors-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 20px;
  max-width: 1200px;
  margin: 0 auto;
}

.error-card {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: var(--shadow);
  cursor: pointer;
  transition: all 0.2s;
  border-left: 4px solid var(--danger);
}

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

.error-code {
  font-size: 14px;
  color: var(--danger);
  font-weight: 600;
  margin-bottom: 8px;
}

.error-title {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 8px;
}

.error-preview {
  color: var(--text-muted);
  font-size: 14px;
  line-height: 1.5;
}

/* Calculator */
.calculator-card {
  max-width: 500px;
  margin: 0 auto;
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 32px;
  box-shadow: var(--shadow-md);
}

.form-group {
  margin-bottom: 20px;
}

.form-group label {
  display: block;
  font-size: 14px;
  font-weight: 500;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.input-select {
  width: 100%;
  padding: 12px 16px;
  font-size: 15px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--card-bg);
  cursor: pointer;
}

.input-select:focus {
  outline: none;
  border-color: var(--primary);
}

.calc-result {
  margin-top: 24px;
  padding: 20px;
  background: var(--primary-light);
  border-radius: var(--radius-sm);
  border-left: 4px solid var(--primary);
}

.calc-result h3 {
  font-size: 16px;
  margin-bottom: 12px;
  color: var(--primary);
}

.result-row {
  display: flex;
  justify-content: space-between;
  padding: 8px 0;
  border-bottom: 1px solid rgba(0, 102, 204, 0.1);
}

.result-row:last-child {
  border-bottom: none;
  font-weight: 600;
  font-size: 18px;
  color: var(--primary);
}

/* Assistant */
.assistant-container {
  max-width: 800px;
  margin: 0 auto;
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow-md);
  display: flex;
  flex-direction: column;
  height: calc(100vh - 200px);
}

.chat-messages {
  flex: 1;
  overflow-y: auto;
  padding: 24px;
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.message {
  display: flex;
  gap: 12px;
  max-width: 85%;
}

.message.user {
  align-self: flex-end;
  flex-direction: row-reverse;
}

.message-avatar {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: var(--primary-light);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  flex-shrink: 0;
}

.message.user .message-avatar {
  background: var(--bg);
}

.message-content {
  background: var(--bg);
  padding: 14px 18px;
  border-radius: var(--radius);
  line-height: 1.6;
}

.message.user .message-content {
  background: var(--primary);
  color: white;
}

.message-content p {
  margin-bottom: 12px;
}

.message-content p:last-child {
  margin-bottom: 0;
}

.message-content ul {
  margin: 12px 0;
  padding-left: 20px;
}

.message-content li {
  margin-bottom: 6px;
}

.chat-input {
  display: flex;
  gap: 12px;
  padding: 16px 24px;
  border-top: 1px solid var(--border);
}

.chat-input .search-input {
  flex: 1;
}

.feedback-block {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px 24px;
  background: var(--bg);
  border-top: 1px solid var(--border);
  justify-content: center;
}

.feedback-btn {
  width: 40px;
  height: 40px;
  font-size: 22px;
  border-radius: 50%;
  background: var(--card-bg);
  border: 1px solid var(--border);
}

.feedback-btn:hover {
  background: var(--primary-light);
  border-color: var(--primary);
}

/* Tests */
.tests-intro {
  max-width: 600px;
  margin: 0 auto;
  text-align: center;
  padding: 60px 24px;
}

.tests-intro p {
  font-size: 18px;
  color: var(--text-muted);
  margin-bottom: 32px;
}

.test-container {
  max-width: 700px;
  margin: 0 auto;
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 32px;
  box-shadow: var(--shadow-md);
}

.test-progress {
  display: flex;
  align-items: center;
  gap: 16px;
  margin-bottom: 24px;
}

.progress-bar {
  flex: 1;
  height: 8px;
  background: var(--bg);
  border-radius: 4px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: var(--primary);
  transition: width 0.3s;
  width: 0%;
}

.test-counter {
  font-size: 14px;
  color: var(--text-muted);
  min-width: 50px;
  text-align: right;
}

.test-question {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 24px;
  line-height: 1.5;
}

.test-answers {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.test-answer {
  padding: 16px 20px;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.2s;
  font-size: 15px;
}

.test-answer:hover {
  border-color: var(--primary);
  background: var(--primary-light);
}

.test-answer.selected {
  border-color: var(--primary);
  background: var(--primary-light);
}

.test-answer.correct {
  border-color: var(--success);
  background: #dcfce7;
}

.test-answer.incorrect {
  border-color: var(--danger);
  background: #fee2e2;
}

.test-feedback {
  margin-top: 20px;
  padding: 16px;
  border-radius: var(--radius-sm);
  background: var(--success);
  color: white;
  display: none;
}

.test-feedback.show {
  display: block;
}

.test-feedback.incorrect {
  background: var(--danger);
}

.test-result {
  max-width: 500px;
  margin: 0 auto;
  text-align: center;
  padding: 60px 24px;
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow-md);
}

.result-score {
  font-size: 64px;
  font-weight: 700;
  color: var(--primary);
  margin: 24px 0;
}

.result-message {
  font-size: 18px;
  color: var(--text-muted);
  margin-bottom: 32px;
}

/* Admin */
.admin-tabs {
  display: flex;
  gap: 8px;
  margin-bottom: 24px;
  flex-wrap: wrap;
}

.admin-tab {
  padding: 10px 20px;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-weight: 500;
  transition: all 0.2s;
}

.admin-tab:hover {
  background: var(--bg);
}

.admin-tab.active {
  background: var(--primary);
  color: white;
  border-color: var(--primary);
}

.admin-content {
  background: var(--card-bg);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
}

.admin-panel {
  display: none;
}

.admin-panel.active {
  display: block;
}

.admin-item {
  padding: 16px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  margin-bottom: 12px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.admin-item-actions {
  display: flex;
  gap: 8px;
}

.admin-btn {
  padding: 6px 12px;
  font-size: 13px;
  border: none;
  border-radius: 6px;
  cursor: pointer;
}

.admin-btn-edit {
  background: var(--primary-light);
  color: var(--primary);
}

.admin-btn-delete {
  background: #fee2e2;
  color: var(--danger);
}

.admin-add-btn {
  margin-bottom: 20px;
}

/* Modal */
.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(0, 0, 0, 0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1000;
  padding: 24px;
}

.modal {
  background: var(--card-bg);
  border-radius: var(--radius);
  width: 100%;
  max-width: 600px;
  max-height: 90vh;
  overflow-y: auto;
  box-shadow: var(--shadow-lg);
}

.modal-large {
  max-width: 800px;
}

.modal-xlarge {
  max-width: 900px;
}

.modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 20px 24px;
  border-bottom: 1px solid var(--border);
}

.modal-header h2 {
  font-size: 20px;
}

.modal-body {
  padding: 24px;
}

.upload-loading {
  text-align: center;
  padding: 40px;
}

.spinner {
  width: 48px;
  height: 48px;
  border: 4px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin: 0 auto 24px;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* Error Modal Content */
.error-detail-section {
  margin-bottom: 24px;
}

.error-detail-section h3 {
  font-size: 16px;
  color: var(--text);
  margin-bottom: 12px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.error-detail-section h3::before {
  content: '';
  width: 4px;
  height: 20px;
  background: var(--primary);
  border-radius: 2px;
}

.error-detail-content {
  background: var(--bg);
  padding: 16px;
  border-radius: var(--radius-sm);
  line-height: 1.7;
}

.error-steps {
  list-style: none;
  counter-reset: step-counter;
}

.error-steps li {
  position: relative;
  padding-left: 36px;
  margin-bottom: 12px;
  counter-increment: step-counter;
}

.error-steps li::before {
  content: counter(step-counter);
  position: absolute;
  left: 0;
  top: 2px;
  width: 24px;
  height: 24px;
  background: var(--primary);
  color: white;
  border-radius: 50%;
  font-size: 12px;
  font-weight: 600;
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Responsive */
@media (max-width: 1024px) {
  .main-content {
    margin-left: 0;
    padding: 24px 16px;
  }

  .sidebar {
    transform: translateX(-100%);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .close-sidebar {
    display: flex;
  }

  .mobile-header {
    display: flex;
  }
}

@media (max-width: 600px) {
  .hero-title {
    font-size: 28px;
  }

  .search-box {
    flex-direction: column;
  }

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

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

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

  .modal {
    margin: 16px;
    max-height: calc(100vh - 32px);
  }
}