/* ===== CSS Variables ===== */
:root {
  --color-primary: #667eea;
  --color-secondary: #764ba2;
  --color-bg: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --color-bg-word: linear-gradient(135deg, #2b5876 0%, #4e4376 100%);
  --color-bg-powerpoint: linear-gradient(135deg, #d5733c 0%, #c44a2a 100%);
  --color-bg-kumir: linear-gradient(135deg, #11998e 0%, #38ef7d 100%);
  --color-white: rgba(255, 255, 255, 0.95);
  --color-text: #555;
  --color-heading: #333;
  --color-success: #4caf50;
  --color-warning: #ff9800;
  --color-info: #2196f3;
  --color-danger: #e53935;
  --shadow-card: 0 10px 30px rgba(0, 0, 0, 0.2);
  --shadow-btn: 0 4px 15px rgba(0, 0, 0, 0.2);
  --radius-card: 15px;
  --radius-btn: 25px;
  --radius-sm: 12px;
  --radius-xs: 8px;
  --transition-fast: 0.3s;
  --transition-slow: 0.5s;
  --font-mono: "Courier New", monospace;
  --font-sans: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  --max-width: 1000px;
}

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

/* ===== Body ===== */
body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  min-height: 100vh;
  padding: 20px;
}

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

/* ===== Headings ===== */
h1 {
  text-align: center;
  color: white;
  margin-bottom: 20px;
  text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
  font-size: 2rem;
}

h2 {
  color: var(--color-heading);
  margin-bottom: 15px;
  font-size: 1.4rem;
  display: flex;
  align-items: center;
  gap: 10px;
}

h3 {
  color: #444;
  margin: 20px 0 10px;
  font-size: 1.2rem;
}

h4 {
  margin-bottom: 10px;
}

p {
  color: var(--color-text);
  line-height: 1.8;
  margin-bottom: 12px;
}

ul, ol {
  margin: 10px 0 15px 25px;
  color: var(--color-text);
  line-height: 1.8;
}

li {
  margin-bottom: 8px;
}

a {
  color: inherit;
}

strong {
  color: #444;
}

/* ===== Navigation ===== */
.nav-links {
  display: flex;
  gap: 15px;
  margin-bottom: 25px;
  flex-wrap: wrap;
  align-items: center;
}

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: rgba(255, 255, 255, 0.2);
  color: white;
  text-decoration: none;
  padding: 12px 20px;
  border-radius: var(--radius-btn);
  transition: background var(--transition-fast);
  font-weight: 500;
}

.back-link:hover,
.back-link:focus {
  background: rgba(255, 255, 255, 0.35);
  outline: none;
}

/* ===== Topic Navigation (prev/next) ===== */
.topic-nav {
  display: flex;
  justify-content: space-between;
  gap: 15px;
  margin-bottom: 25px;
  flex-wrap: wrap;
}

.topic-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: rgba(255, 255, 255, 0.2);
  color: white;
  text-decoration: none;
  padding: 12px 20px;
  border-radius: var(--radius-btn);
  transition: background var(--transition-fast), transform var(--transition-fast);
  font-weight: 500;
  border: none;
  cursor: pointer;
}

.topic-nav-btn:hover,
.topic-nav-btn:focus {
  background: rgba(255, 255, 255, 0.35);
  transform: translateY(-2px);
  outline: none;
}

.topic-nav-btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
  transform: none;
}

.topic-nav-spacer {
  flex: 1;
}

/* ===== Cards / Sections ===== */
.theory-section {
  background: var(--color-white);
  border-radius: var(--radius-card);
  padding: 25px;
  margin-bottom: 25px;
  box-shadow: var(--shadow-card);
}

/* ===== Apps Grid (index page) ===== */
.apps-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 25px;
  margin-bottom: 40px;
}

.app-card {
  background: var(--color-white);
  border-radius: var(--radius-card);
  padding: 30px 25px;
  text-decoration: none;
  box-shadow: var(--shadow-card);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  border-top: 5px solid var(--color-primary);
}

.app-card:hover,
.app-card:focus {
  transform: translateY(-5px);
  box-shadow: 0 15px 40px rgba(0, 0, 0, 0.3);
  outline: none;
}

.app-card .icon {
  font-size: 3rem;
  margin-bottom: 15px;
}

.app-card h3 {
  color: var(--color-heading);
  margin-bottom: 8px;
  font-size: 1.3rem;
}

.app-card p {
  color: #777;
  font-size: 0.95rem;
  margin-bottom: 12px;
}

.app-card .action-link {
  color: var(--color-primary);
  font-weight: 600;
  margin-top: auto;
}

.app-card.word {
  border-top-color: #2b5876;
}

.app-card.excel {
  border-top-color: #217346;
}

.app-card.powerpoint {
  border-top-color: #d24726;
}

/* Subtitle on home page */
.subtitle {
  text-align: center;
  color: rgba(255, 255, 255, 0.9);
  font-size: 1.1rem;
  margin-bottom: 30px;
  max-width: 800px;
  margin-left: auto;
  margin-right: auto;
}

/* ===== Formula Box ===== */
.formula-box {
  background: linear-gradient(145deg, #f5f7fa 0%, #e4e8eb 100%);
  border-radius: var(--radius-sm);
  padding: 20px;
  margin: 15px 0;
  border-left: 4px solid var(--color-primary);
  text-align: center;
}

.formula {
  font-size: 1.3rem;
  font-weight: bold;
  color: var(--color-heading);
  font-family: var(--font-mono);
}

.formula-description {
  font-size: 0.95rem;
  color: #666;
  margin-top: 10px;
}

/* ===== Example / Tip / Warning Boxes ===== */
.example-box {
  background: #e8f5e9;
  border-radius: var(--radius-sm);
  padding: 20px;
  margin: 15px 0;
  border-left: 4px solid var(--color-success);
}

.example-box h4 {
  color: #2e7d32;
}

.example-box p {
  color: var(--color-heading);
}

.example-solution {
  background: white;
  border-radius: var(--radius-xs);
  padding: 15px;
  margin-top: 10px;
  font-family: var(--font-mono);
  font-size: 0.95rem;
}

.tip-box {
  background: #e3f2fd;
  border-radius: var(--radius-sm);
  padding: 20px;
  margin: 15px 0;
  border-left: 4px solid var(--color-info);
}

.tip-box h4 {
  color: #1565c0;
}

.warning-box {
  background: #fff3e0;
  border-radius: var(--radius-sm);
  padding: 20px;
  margin: 15px 0;
  border-left: 4px solid var(--color-warning);
}

.warning-box h4 {
  color: #e65100;
}

/* ===== Function Syntax ===== */
.function-syntax {
  background: #f8f9fa;
  border-radius: var(--radius-sm);
  padding: 20px;
  margin: 15px 0;
  border-left: 4px solid #28a745;
}

.function-syntax h4 {
  color: #28a745;
}

/* ===== Tables ===== */
.units-table,
.comparison-table {
  width: 100%;
  border-collapse: collapse;
  margin: 15px 0;
}

.units-table th,
.units-table td,
.comparison-table th,
.comparison-table td {
  padding: 12px 15px;
  text-align: left;
  border: 1px solid #ddd;
  border-bottom: 1px solid #ddd;
}

.units-table th,
.comparison-table th {
  background: linear-gradient(145deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
  font-weight: 600;
}

.units-table tr:hover,
.comparison-table tr:hover {
  background: #f5f5f5;
}

.comparison-table tr:nth-child(even) {
  background: #f9f9f9;
}

.comparison-table tr:nth-child(even):hover {
  background: #f0f0f0;
}

.units-table td:first-child {
  font-weight: 600;
  color: var(--color-primary);
}

/* ===== Progress Tracker ===== */
.progress-bar-container {
  background: rgba(255, 255, 255, 0.2);
  border-radius: 10px;
  padding: 10px 15px;
  margin-bottom: 25px;
  display: flex;
  align-items: center;
  gap: 12px;
  color: white;
  font-size: 0.9rem;
}

.progress-bar {
  flex: 1;
  height: 8px;
  background: rgba(255, 255, 255, 0.3);
  border-radius: 4px;
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  background: #38ef7d;
  border-radius: 4px;
  transition: width 0.5s ease;
}

.progress-text {
  white-space: nowrap;
  font-weight: 600;
  min-width: 45px;
  text-align: right;
}

/* ===== Quick Nav ===== */
.quick-nav {
  position: fixed;
  bottom: 20px;
  right: 20px;
  display: flex;
  flex-direction: column;
  gap: 10px;
  z-index: 100;
}

.quick-nav-btn {
  width: 50px;
  height: 50px;
  border-radius: 50%;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
  transition: transform var(--transition-fast);
  box-shadow: var(--shadow-btn);
  display: flex;
  align-items: center;
  justify-content: center;
}

.quick-nav-btn:hover,
.quick-nav-btn:focus {
  transform: scale(1.1);
  outline: none;
}

.quick-nav-btn.top {
  background: linear-gradient(145deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
}

.quick-nav-btn.practice {
  background: linear-gradient(145deg, #11998e 0%, #38ef7d 100%);
  color: white;
}

.quick-nav-btn.theory {
  background: linear-gradient(145deg, #667eea 0%, #764ba2 100%);
  color: white;
}

/* ===== Intro section ===== */
.intro-section {
  background: var(--color-white);
  border-radius: var(--radius-card);
  padding: 25px;
  margin-bottom: 25px;
  box-shadow: var(--shadow-card);
}

.intro-section h2 {
  color: var(--color-heading);
  margin-bottom: 15px;
}

.intro-section ul {
  color: var(--color-text);
}

/* ===== Highlights & Code ===== */
.highlight {
  background: linear-gradient(145deg, #fff9c4 0%, #fff59d 100%);
  padding: 2px 6px;
  border-radius: 4px;
  font-weight: 600;
}

.code {
  background: #f5f5f5;
  padding: 2px 8px;
  border-radius: 4px;
  font-family: var(--font-mono);
  font-size: 0.9rem;
}

/* ===== Index page styles (office-web specific) ===== */
.page-index .app-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 25px;
  margin-bottom: 40px;
}

.page-index .app-card {
  background: var(--color-white);
  border-radius: var(--radius-card);
  padding: 30px 25px;
  text-decoration: none;
  box-shadow: var(--shadow-card);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
}

.page-index .app-card:hover,
.page-index .app-card:focus {
  transform: translateY(-5px);
  box-shadow: 0 15px 40px rgba(0, 0, 0, 0.3);
  outline: none;
}

.page-index .app-card-icon {
  font-size: 3rem;
  margin-bottom: 15px;
}

.page-index .app-card h2 {
  color: var(--color-heading);
  margin-bottom: 8px;
  display: block;
}

.page-index .app-card p {
  color: #777;
  font-size: 0.95rem;
}

/* ===== Functions Grid (Excel/Calc function cards) ===== */
.functions-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
  margin: 20px 0;
}

.function-card {
  background: white;
  border-radius: var(--radius-sm);
  padding: 20px;
  text-decoration: none;
  box-shadow: 0 3px 12px rgba(0, 0, 0, 0.1);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  display: flex;
  flex-direction: column;
  border-left: 4px solid var(--color-primary);
}

.function-card:hover,
.function-card:focus {
  transform: translateY(-3px);
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
  outline: none;
}

.function-card h4 {
  color: var(--color-heading);
  margin-bottom: 6px;
  font-size: 1.1rem;
}

.function-card p {
  color: #777;
  font-size: 0.9rem;
  margin-bottom: 8px;
  flex: 1;
}

.function-card .function-link {
  color: var(--color-primary);
  font-weight: 600;
  font-size: 0.9rem;
  margin-top: auto;
}

.function-link {
  color: var(--color-primary);
  font-weight: 600;
  text-decoration: none;
}

.function-link:hover,
.function-link:focus {
  text-decoration: underline;
  outline: none;
}

/* ===== Feature Grid (used on Word, PowerPoint, Excel pages) ===== */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 20px;
  margin: 20px 0;
}

.feature-card {
  background: white;
  border-radius: var(--radius-sm);
  padding: 20px;
  text-decoration: none;
  box-shadow: 0 3px 12px rgba(0, 0, 0, 0.1);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  display: flex;
  flex-direction: column;
  border-left: 4px solid var(--color-primary);
}

.feature-card:hover,
.feature-card:focus {
  transform: translateY(-3px);
  box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
  outline: none;
}

.feature-card h4 {
  color: var(--color-heading);
  margin-bottom: 6px;
  font-size: 1.1rem;
}

.feature-card p {
  color: #777;
  font-size: 0.9rem;
  margin-bottom: 8px;
  flex: 1;
}

/* ===== Step Cards (algorithm steps, e.g., oge14-trainer) ===== */
.step-card {
  display: flex;
  gap: 15px;
  margin-bottom: 15px;
  padding: 15px;
  background: #f8f9fa;
  border-radius: var(--radius-xs);
  border-left: 4px solid var(--color-primary);
  align-items: flex-start;
}

.step-num {
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: linear-gradient(145deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
  font-weight: 700;
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.step-text {
  flex: 1;
  color: var(--color-text);
  line-height: 1.6;
}

.step-text ul {
  margin: 8px 0 0 20px;
}

/* ===== Formula Block (oge14-trainer) ===== */
.formula-block {
  background: #f0f4ff;
  border-radius: var(--radius-xs);
  padding: 15px;
  margin: 12px 0;
  border-left: 4px solid #667eea;
}

.formula-desc {
  font-size: 0.95rem;
  color: #666;
  margin-top: 8px;
  line-height: 1.6;
}

/* ===== Data Table Sample (sample spreadsheet data) ===== */
.data-table-sample {
  width: 100%;
  border-collapse: collapse;
  margin: 15px 0;
  font-size: 0.9rem;
}

.data-table-sample th,
.data-table-sample td {
  padding: 8px 12px;
  border: 1px solid #ccc;
  text-align: center;
  background: #fff;
}

.data-table-sample th {
  background: #e8ecf1;
  font-weight: 600;
  color: var(--color-heading);
}

.data-table-sample tr:nth-child(even) td {
  background: #f7f8fa;
}

.data-table-sample tr:hover td {
  background: #eef1f5;
}

/* ===== Generic Table inside theory-section ===== */
.theory-section table {
  width: 100%;
  border-collapse: collapse;
  margin: 15px 0;
}

.theory-section table th,
.theory-section table td {
  padding: 10px 14px;
  border: 1px solid #ddd;
  text-align: left;
  font-size: 0.95rem;
}

.theory-section table th {
  background: linear-gradient(145deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
  font-weight: 600;
}

.theory-section table tr:nth-child(even) td {
  background: #f9f9f9;
}

.theory-section table tr:hover td {
  background: #f0f0f0;
}

/* ===== Trainer Styles ===== */
.trainer-container {
  background: var(--color-white);
  border-radius: var(--radius-card);
  padding: 30px;
  margin-bottom: 25px;
  box-shadow: var(--shadow-card);
}

.trainer-question {
  font-size: 1.2rem;
  margin-bottom: 20px;
  color: var(--color-heading);
}

.trainer-input {
  width: 100%;
  padding: 15px;
  border: 2px solid #ddd;
  border-radius: var(--radius-xs);
  font-size: 1.1rem;
  font-family: var(--font-mono);
  margin-bottom: 15px;
  transition: border-color var(--transition-fast);
}

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

.trainer-input.correct {
  border-color: var(--color-success);
  background: #e8f5e9;
}

.trainer-input.incorrect {
  border-color: var(--color-danger);
  background: #ffebee;
}

.trainer-btn {
  padding: 12px 30px;
  background: linear-gradient(145deg, var(--color-primary) 0%, var(--color-secondary) 100%);
  color: white;
  border: none;
  border-radius: var(--radius-btn);
  font-size: 1rem;
  cursor: pointer;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
  font-weight: 500;
}

.trainer-btn:hover,
.trainer-btn:focus {
  transform: translateY(-2px);
  box-shadow: var(--shadow-btn);
  outline: none;
}

.trainer-feedback {
  margin-top: 15px;
  padding: 15px;
  border-radius: var(--radius-xs);
  font-weight: 500;
  display: none;
}

.trainer-feedback.correct {
  display: block;
  background: #e8f5e9;
  color: #2e7d32;
}

.trainer-feedback.incorrect {
  display: block;
  background: #ffebee;
  color: #c62828;
}

.trainer-score {
  text-align: center;
  margin-top: 20px;
  font-size: 1.1rem;
  color: var(--color-heading);
}

.trainer-score span {
  font-weight: 700;
  color: var(--color-primary);
}

/* ===== Certificates / Score ===== */
.score-display {
  background: linear-gradient(145deg, #667eea 0%, #764ba2 100%);
  color: white;
  padding: 20px;
  border-radius: var(--radius-sm);
  text-align: center;
  margin: 15px 0;
  font-size: 1.1rem;
}

.score-display .score-value {
  font-size: 2rem;
  font-weight: 700;
}

/* ===== Mini-Test ===== */
.test-question {
  margin: 20px 0;
  padding: 15px;
  background: var(--color-bg);
  border-radius: var(--radius-xs);
  border: 1px solid var(--color-border);
}

.test-q {
  margin-bottom: 10px;
  color: var(--color-heading);
}

.test-option {
  display: block;
  padding: 8px 12px;
  margin: 4px 0;
  cursor: pointer;
  border-radius: var(--radius-xs);
  transition: background var(--transition-fast);
  font-size: 0.95rem;
}

.test-option:hover {
  background: var(--color-bg-alt, #f0f0f0);
}

.test-option input[type="radio"] {
  margin-right: 8px;
  accent-color: var(--color-primary);
}

.test-option.selected {
  background: #e3f2fd;
  border: 1px solid var(--color-primary);
}

.test-option.correct-answer {
  background: #e8f5e9;
  border: 1px solid #2e7d32;
}

.test-option.wrong-answer {
  background: #ffebee;
  border: 1px solid #c62828;
}

.test-result {
  font-weight: 500;
  font-size: 1rem;
}

/* ===== Print styles ===== */
@media print {
  .quick-nav,
  .nav-links,
  .topic-nav,
  .progress-bar-container {
    display: none;
  }
}

/* ===== Mobile: 1024px ===== */
@media (max-width: 1024px) {
  .container {
    max-width: 95%;
  }

  .apps-grid {
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  }
}

/* ===== Mobile: 768px (tablets) ===== */
@media (max-width: 768px) {
  body {
    padding: 15px;
  }

  h1 {
    font-size: 1.6rem;
  }

  .apps-grid {
    grid-template-columns: 1fr;
    gap: 15px;
  }

  .topic-nav {
    flex-direction: column;
    align-items: stretch;
  }

  .nav-links {
    flex-direction: column;
    align-items: stretch;
  }

  .theory-section,
  .trainer-container {
    padding: 20px 15px;
  }

  .comparison-table th,
  .comparison-table td,
  .units-table th,
  .units-table td {
    padding: 8px 10px;
    font-size: 0.9rem;
  }
}

/* ===== Mobile: 600px ===== */
@media (max-width: 600px) {
  h1 {
    font-size: 1.5rem;
  }

  .theory-section {
    padding: 20px 15px;
  }

  .formula {
    font-size: 1.1rem;
  }

  .units-table th,
  .units-table td {
    padding: 8px 10px;
    font-size: 0.9rem;
  }

  .comparison-table th,
  .comparison-table td {
    padding: 10px;
    font-size: 0.9rem;
  }

  .trainer-container {
    padding: 20px 15px;
  }

  .trainer-input {
    font-size: 1rem;
    padding: 12px;
  }
}

/* ===== Mobile: 480px ===== */
@media (max-width: 480px) {
  body {
    padding: 10px;
  }

  h1 {
    font-size: 1.3rem;
  }

  h2 {
    font-size: 1.1rem;
  }

  h3 {
    font-size: 1rem;
  }

  .back-link,
  .topic-nav-btn {
    padding: 10px 15px;
    font-size: 0.9rem;
  }

  .app-card {
    padding: 20px 15px;
  }

  .app-card-icon {
    font-size: 2.5rem;
  }

  .formula-box {
    padding: 15px;
  }

  .formula {
    font-size: 1rem;
  }

  .quick-nav-btn {
    width: 40px;
    height: 40px;
    font-size: 1rem;
  }

  .progress-bar-container {
    flex-wrap: wrap;
    font-size: 0.8rem;
  }
}