/* 
   HSK Level 5 Study Platform
   Main Stylesheet
*/

/* ===== Base Styles ===== */
:root {
  /* Color Palette */
  --primary-color: #3498db;       /* Blue: trustworthy, focus */
  --primary-dark: #2980b9;        /* Darker blue for hover states */
  --secondary-color: #2ecc71;     /* Green: growth, learning */
  --secondary-dark: #27ae60;      /* Darker green for hover states */
  --accent-color: #f1c40f;        /* Yellow: energy, interaction */
  --accent-dark: #f39c12;         /* Darker yellow for hover states */
  --text-primary: #333333;        /* Dark gray for main text */
  --text-secondary: #666666;      /* Medium gray for secondary text */
  --text-light: #ffffff;          /* White text for dark backgrounds */
  --bg-light: #ffffff;            /* White background */
  --bg-off-white: #f9f9f9;        /* Off-white for alternating sections */
  --bg-gray: #f2f2f2;             /* Light gray for cards, inputs */
  --border-color: #e0e0e0;        /* Light gray for borders */
  --shadow-color: rgba(0, 0, 0, 0.1); /* Shadow color */
  --success-color: #2ecc71;       /* Green for success messages */
  --error-color: #e74c3c;         /* Red for error messages */
  
  /* Typography */
  --font-primary: 'Poppins', sans-serif;
  --font-chinese: 'Noto Sans SC', sans-serif;
  
  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-xxl: 3rem;
  
  /* Border Radius */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  
  /* Transitions */
  --transition-fast: 0.2s ease;
  --transition-normal: 0.3s ease;
}

/* Reset and Base Styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-primary);
  color: var(--text-primary);
  line-height: 1.6;
  background-color: var(--bg-light);
}

.chinese-text {
  font-family: var(--font-chinese);
}

h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  margin-bottom: var(--spacing-md);
}

p {
  margin-bottom: var(--spacing-md);
}

a {
  color: var(--primary-color);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--primary-dark);
}

ul {
  list-style: none;
}

img {
  max-width: 100%;
  height: auto;
}

button, .btn {
  cursor: pointer;
}

/* Container */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

/* ===== Header & Navigation ===== */
.main-header {
  background-color: var(--bg-light);
  box-shadow: 0 2px 10px var(--shadow-color);
  position: sticky;
  top: 0;
  z-index: 100;
}

.main-header .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--spacing-md);
}

.logo h1 {
  font-size: 1.5rem;
  margin-bottom: 0;
  color: var(--primary-color);
}

.logo .chinese-text {
  font-size: 1.2rem;
  color: var(--text-secondary);
  margin-left: var(--spacing-xs);
}

.main-nav {
  display: flex;
  align-items: center;
}

.nav-list {
  display: flex;
  gap: var(--spacing-lg);
}

.nav-list a {
  color: var(--text-primary);
  font-weight: 500;
  padding: var(--spacing-xs) var(--spacing-sm);
  border-bottom: 2px solid transparent;
  transition: all var(--transition-fast);
}

.nav-list a:hover, .nav-list a.active {
  color: var(--primary-color);
  border-bottom-color: var(--primary-color);
}

.mobile-menu-toggle {
  display: none;
  background: none;
  border: none;
  flex-direction: column;
  justify-content: space-between;
  width: 30px;
  height: 21px;
}

.mobile-menu-toggle .bar {
  height: 3px;
  width: 100%;
  background-color: var(--text-primary);
  border-radius: 10px;
  transition: all var(--transition-normal);
}

/* ===== Buttons ===== */
.btn {
  display: inline-block;
  padding: var(--spacing-sm) var(--spacing-lg);
  border-radius: var(--radius-md);
  font-weight: 500;
  text-align: center;
  transition: all var(--transition-fast);
  border: none;
  font-size: 1rem;
}

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

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

.btn-secondary {
  background-color: var(--secondary-color);
  color: var(--text-light);
}

.btn-secondary:hover {
  background-color: var(--secondary-dark);
  color: var(--text-light);
}

.btn-outline {
  background-color: transparent;
  border: 2px solid var(--primary-color);
  color: var(--primary-color);
}

.btn-outline:hover {
  background-color: var(--primary-color);
  color: var(--text-light);
}

/* ===== Hero Section ===== */
.hero-section {
  padding: var(--spacing-xxl) 0;
  background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
  color: var(--text-light);
}

.hero-content {
  text-align: center;
  max-width: 800px;
  margin: 0 auto var(--spacing-xl);
}

.hero-content h2 {
  font-size: 2.5rem;
  margin-bottom: var(--spacing-md);
}

.hero-content p {
  font-size: 1.2rem;
  margin-bottom: var(--spacing-lg);
}

.hero-buttons {
  display: flex;
  justify-content: center;
  gap: var(--spacing-md);
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: var(--spacing-xl);
  margin-top: var(--spacing-xl);
}

.stat-box {
  text-align: center;
  background-color: rgba(255, 255, 255, 0.1);
  padding: var(--spacing-md);
  border-radius: var(--radius-md);
  min-width: 150px;
}

.stat-number {
  display: block;
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: var(--spacing-xs);
}

.stat-label {
  font-size: 0.9rem;
  opacity: 0.9;
}

/* ===== Section Styles ===== */
.section {
  padding: var(--spacing-xxl) 0;
}

.section:nth-child(even) {
  background-color: var(--bg-off-white);
}

.section-title {
  text-align: center;
  font-size: 2rem;
  margin-bottom: var(--spacing-sm);
  color: var(--text-primary);
}

.section-description {
  text-align: center;
  max-width: 800px;
  margin: 0 auto var(--spacing-xl);
  color: var(--text-secondary);
}

/* ===== Dashboard Section ===== */
.dashboard-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
}

.dashboard-card {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  box-shadow: 0 2px 10px var(--shadow-color);
  text-align: center;
  transition: transform var(--transition-normal);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  height: 100%;
}

.dashboard-card:hover {
  transform: translateY(-5px);
}

.dashboard-icon {
  font-size: 2.5rem;
  margin-bottom: var(--spacing-md);
}

.dashboard-card h3 {
  color: var(--primary-color);
  margin-bottom: var(--spacing-sm);
}

.dashboard-card p {
  color: var(--text-secondary);
  margin-bottom: var(--spacing-lg);
  flex-grow: 1;
}

.study-tips {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  box-shadow: 0 2px 10px var(--shadow-color);
}

.study-tips h3 {
  text-align: center;
  margin-bottom: var(--spacing-md);
  color: var(--primary-color);
}

.tips-list {
  list-style-type: disc;
  padding-left: var(--spacing-xl);
}

.tips-list li {
  margin-bottom: var(--spacing-md);
  color: var(--text-secondary);
}

.tips-list li strong {
  color: var(--text-primary);
}

/* ===== Flashcards Section ===== */
.flashcard-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: var(--spacing-xl);
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

.control-group {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.select-control {
  padding: var(--spacing-sm) var(--spacing-md);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  background-color: var(--bg-light);
  font-family: var(--font-primary);
  font-size: 1rem;
}

.flashcard-container {
  max-width: 600px;
  margin: 0 auto;
}

.flashcard {
  perspective: 1000px;
  height: 300px;
  margin-bottom: var(--spacing-lg);
}

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  text-align: center;
  transition: transform 0.6s;
  transform-style: preserve-3d;
  box-shadow: 0 4px 8px var(--shadow-color);
  border-radius: var(--radius-lg);
}

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

.flashcard-front, .flashcard-back {
  position: absolute;
  width: 100%;
  height: 100%;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: var(--spacing-lg);
  border-radius: var(--radius-lg);
}

.flashcard-front {
  background-color: var(--primary-color);
  color: var(--text-light);
}

.flashcard-back {
  background-color: var(--bg-light);
  color: var(--text-primary);
  transform: rotateY(180deg);
  border: 1px solid var(--border-color);
}

.chinese-character {
  font-family: var(--font-chinese);
  font-size: 3rem;
  margin-bottom: var(--spacing-md);
}

.pinyin {
  font-size: 1.5rem;
}

.english-meaning {
  font-size: 1.8rem;
  margin-bottom: var(--spacing-md);
}

.example-sentence {
  font-size: 1rem;
  line-height: 1.6;
}

.example-sentence p {
  margin-bottom: var(--spacing-xs);
}

.example-sentence .chinese {
  font-family: var(--font-chinese);
  font-weight: 500;
}

.flashcard-navigation {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: var(--spacing-lg);
}

.nav-btn {
  background-color: var(--primary-color);
  color: var(--text-light);
  border: none;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  font-size: 1.2rem;
  display: flex;
  justify-content: center;
  align-items: center;
  transition: background-color var(--transition-fast);
}

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

.card-counter {
  font-size: 0.9rem;
  color: var(--text-secondary);
}

/* ===== Quizzes Section ===== */
.quiz-types {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
}

.quiz-card {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  box-shadow: 0 2px 10px var(--shadow-color);
  transition: transform var(--transition-normal);
}

.quiz-card:hover {
  transform: translateY(-5px);
}

.quiz-card h3 {
  color: var(--primary-color);
  margin-bottom: var(--spacing-sm);
}

.quiz-card p {
  margin-bottom: var(--spacing-lg);
  color: var(--text-secondary);
}

.quiz-preview {
  background-color: var(--bg-gray);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  max-width: 800px;
  margin: 0 auto;
}

.quiz-preview h3 {
  margin-bottom: var(--spacing-md);
  text-align: center;
}

.quiz-question p {
  font-family: var(--font-chinese);
  font-size: 1.2rem;
  margin-bottom: var(--spacing-lg);
  text-align: center;
}

.quiz-options {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-md);
}

.option {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-sm);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  transition: background-color var(--transition-fast);
}

.option:hover {
  background-color: var(--bg-light);
}

.option label {
  font-family: var(--font-chinese);
  cursor: pointer;
  flex-grow: 1;
}

/* Quiz Results Styles */
.quiz-results {
  text-align: center;
  margin-bottom: var(--spacing-lg);
}

.quiz-score {
  font-size: 1.2rem;
  font-weight: 600;
  margin-bottom: var(--spacing-sm);
}

.quiz-percentage {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
}

.quiz-review h4 {
  margin-top: var(--spacing-lg);
  margin-bottom: var(--spacing-md);
  text-align: center;
}

.quiz-answer {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-md);
  margin-bottom: var(--spacing-md);
  border-left: 4px solid var(--border-color);
}

.quiz-answer.correct {
  border-left-color: var(--success-color);
}

.quiz-answer.incorrect {
  border-left-color: var(--error-color);
}

.question-number {
  font-weight: 600;
  margin-bottom: var(--spacing-xs);
}

.question-prompt {
  margin-bottom: var(--spacing-sm);
}

.user-answer, .correct-answer {
  margin-bottom: var(--spacing-xs);
}

.user-answer {
  color: var(--text-secondary);
}

.correct-answer {
  font-weight: 500;
}

.explanation {
  font-style: italic;
  color: var(--text-secondary);
}

/* ===== Reading Section ===== */
.reading-filters {
  display: flex;
  justify-content: center;
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
  flex-wrap: wrap;
}

.filter-group {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

.reading-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--spacing-lg);
}

.reading-card {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  box-shadow: 0 2px 10px var(--shadow-color);
  transition: transform var(--transition-normal);
}

.reading-card:hover {
  transform: translateY(-5px);
}

.reading-card h3 {
  font-family: var(--font-chinese);
  color: var(--text-primary);
  margin-bottom: var(--spacing-xs);
}

.reading-meta {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-bottom: var(--spacing-md);
}

.reading-excerpt {
  font-family: var(--font-chinese);
  margin-bottom: var(--spacing-lg);
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

/* Reading Exercise Styles */
.reading-exercise {
  max-width: 800px;
  margin: 0 auto;
}

.reading-header {
  margin-bottom: var(--spacing-lg);
  position: relative;
}

.reading-header h2 {
  font-family: var(--font-chinese);
  text-align: center;
  margin-top: var(--spacing-md);
}

.back-btn {
  position: absolute;
  top: 0;
  left: 0;
}

.reading-controls {
  display: flex;
  justify-content: center;
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-lg);
}

.toggle-control {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  cursor: pointer;
}

.toggle-control input {
  margin: 0;
}

.reading-content {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
  box-shadow: 0 2px 10px var(--shadow-color);
}

.chinese-text {
  font-family: var(--font-chinese);
  font-size: 1.2rem;
  line-height: 1.8;
  margin-bottom: var(--spacing-md);
}

.pinyin-text {
  font-size: 1rem;
  line-height: 1.8;
  color: var(--text-secondary);
  margin-bottom: var(--spacing-md);
}

.english-text {
  font-size: 1rem;
  line-height: 1.6;
  border-top: 1px solid var(--border-color);
  padding-top: var(--spacing-md);
}

.vocabulary-section, .comprehension-section {
  margin-bottom: var(--spacing-xl);
}

.vocabulary-section h3, .comprehension-section h3 {
  text-align: center;
  margin-bottom: var(--spacing-lg);
}

.vocabulary-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--spacing-md);
}

.vocab-item {
  background-color: var(--bg-light);
  border-radius: var(--radius-sm);
  padding: var(--spacing-sm);
  border: 1px solid var(--border-color);
  display: flex;
  flex-direction: column;
}

.vocab-word {
  font-family: var(--font-chinese);
  font-weight: 600;
  font-size: 1.1rem;
}

.vocab-pinyin {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-bottom: var(--spacing-xs);
}

.vocab-english {
  font-style: italic;
}

.comprehension-questions {
  margin-bottom: var(--spacing-lg);
}

.question {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  margin-bottom: var(--spacing-lg);
  box-shadow: 0 2px 5px var(--shadow-color);
}

.question-text {
  font-family: var(--font-chinese);
  font-weight: 600;
  font-size: 1.1rem;
  margin-bottom: var(--spacing-xs);
}

.question-pinyin {
  color: var(--text-secondary);
  font-size: 0.9rem;
  margin-bottom: var(--spacing-xs);
}

.question-english {
  font-style: italic;
  margin-bottom: var(--spacing-md);
  border-bottom: 1px solid var(--border-color);
  padding-bottom: var(--spacing-sm);
}

.question-options {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.question-options .option {
  padding: var(--spacing-sm) var(--spacing-md);
}

.option-chinese {
  font-family: var(--font-chinese);
  font-weight: 500;
}

.option-pinyin, .option-english {
  display: block;
  font-size: 0.9rem;
  color: var(--text-secondary);
}

.feedback {
  margin-top: var(--spacing-md);
  padding: var(--spacing-sm);
  border-radius: var(--radius-sm);
  font-weight: 500;
}

.feedback.correct {
  background-color: rgba(46, 204, 113, 0.1);
  color: var(--success-color);
}

.feedback.incorrect {
  background-color: rgba(231, 76, 60, 0.1);
  color: var(--error-color);
}

.score-display {
  text-align: center;
  margin: var(--spacing-lg) 0;
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--primary-color);
}

.check-answers-btn {
  display: block;
  margin: 0 auto;
}

/* ===== Resources Section ===== */
.resources-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--spacing-lg);
}

.resource-card {
  background-color: var(--bg-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-lg);
  box-shadow: 0 2px 10px var(--shadow-color);
  text-align: center;
  transition: transform var(--transition-normal);
}

.resource-card:hover {
  transform: translateY(-5px);
}

.resource-icon {
  font-size: 2.5rem;
  margin-bottom: var(--spacing-md);
}

.resource-card h3 {
  color: var(--primary-color);
  margin-bottom: var(--spacing-sm);
}

.resource-card p {
  color: var(--text-secondary);
  margin-bottom: var(--spacing-lg);
}

.resource-link {
  color: var(--primary-color);
  font-weight: 500;
  position: relative;
}

.resource-link::after {
  content: "→";
  margin-left: var(--spacing-xs);
  transition: transform var(--transition-fast);
  display: inline-block;
}

.resource-link:hover::after {
  transform: translateX(3px);
}

/* ===== Footer ===== */
.main-footer {
  background-color: #2c3e50;
  color: var(--text-light);
  padding: var(--spacing-xl) 0;
}

.footer-content {
  display: flex;
  justify-content: space-between;
  margin-bottom: var(--spacing-xl);
  flex-wrap: wrap;
  gap: var(--spacing-lg);
}

.footer-logo {
  flex-basis: 300px;
}

.footer-logo h2 {
  color: var(--text-light);
  margin-bottom: var(--spacing-sm);
}

.footer-links {
  display: flex;
  gap: var(--spacing-xl);
  flex-wrap: wrap;
}

.footer-column h3 {
  color: var(--accent-color);
  margin-bottom: var(--spacing-md);
  font-size: 1.2rem;
}

.footer-column ul {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.footer-column a {
  color: var(--text-light);
  opacity: 0.8;
  transition: opacity var(--transition-fast);
}

.footer-column a:hover {
  opacity: 1;
  color: var(--accent-color);
}

.footer-bottom {
  text-align: center;
  padding-top: var(--spacing-lg);
  border-top: 1px solid rgba(255, 255, 255, 0.1);
  font-size: 0.9rem;
  opacity: 0.7;
}

/* Error Message */
.error-message {
  background-color: rgba(231, 76, 60, 0.1);
  color: var(--error-color);
  padding: var(--spacing-md);
  border-radius: var(--radius-md);
  text-align: center;
  margin: var(--spacing-lg) 0;
}

/* ===== Responsive Styles ===== */
@media (max-width: 992px) {
  .hero-content h2 {
    font-size: 2rem;
  }
  
  .hero-stats {
    flex-wrap: wrap;
    justify-content: center;
  }
  
  .stat-box {
    flex-basis: 40%;
  }
  
  .quiz-options {
    grid-template-columns: 1fr;
  }
  
  .vocabulary-list {
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  }
}

@media (max-width: 768px) {
  .mobile-menu-toggle {
    display: flex;
  }
  
  .nav-list {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background-color: var(--bg-light);
    flex-direction: column;
    align-items: center;
    padding: var(--spacing-lg) 0;
    box-shadow: 0 4px 6px var(--shadow-color);
    transform: translateY(-150%);
    opacity: 0;
    transition: all var(--transition-normal);
    z-index: 99;
  }
  
  .nav-list.active {
    transform: translateY(0);
    opacity: 1;
  }
  
  .hero-buttons {
    flex-direction: column;
    gap: var(--spacing-sm);
  }
  
  .stat-box {
    flex-basis: 100%;
  }
  
  .flashcard-controls {
    flex-direction: column;
    align-items: stretch;
  }
  
  .control-group {
    justify-content: space-between;
  }
  
  .reading-filters {
    flex-direction: column;
    align-items: stretch;
  }
  
  .reading-controls {
    flex-direction: column;
    align-items: center;
  }
  
  .footer-content {
    flex-direction: column;
  }
  
  .footer-links {
    width: 100%;
    justify-content: space-between;
  }
}

@media (max-width: 576px) {
  html {
    font-size: 14px;
  }
  
  .section {
    padding: var(--spacing-xl) 0;
  }
  
  .hero-section {
    padding: var(--spacing-xl) 0;
  }
  
  .flashcard {
    height: 250px;
  }
  
  .chinese-character {
    font-size: 2.5rem;
  }
  
  .footer-links {
    flex-direction: column;
    gap: var(--spacing-lg);
  }
  
  .reading-header .back-btn {
    position: static;
    margin-bottom: var(--spacing-md);
  }
}