/* CSS Reset and Variables */
:root {
  --primary: #f26522;
  --primary-dark: #d85419;
  --primary-light: #ff7d3a;
  --primary-bg: rgba(242, 101, 34, 0.08);
  
  --text-primary: #1a1a1a;
  --text-secondary: #4a4a4a;
  --text-muted: #8a8a8a;
  --text-inverse: #ffffff;
  
  --bg-primary: #ffffff;
  --bg-secondary: #f9fafb;
  --bg-tertiary: #f3f4f6;
  
  --border-light: #e5e7eb;
  --border-medium: #d1d5db;
  --border-dark: #9ca3af;
  
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.07);
  --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.1);
  
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  
  --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-fast: all 0.15s cubic-bezier(0.4, 0, 0.2, 1);
  
  --font-primary: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-secondary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-primary);
  color: var(--text-primary);
  background: var(--bg-secondary);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* Loading Screen */
.loader {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: var(--bg-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 9999;
  transition: opacity 0.3s ease;
}

.loader.hidden {
  opacity: 0;
  pointer-events: none;
}

.loader-content {
  text-align: center;
}

.loader-logo {
  margin-bottom: 24px;
  animation: pulse 1.5s ease infinite;
}

.logo-text {
  font-family: var(--font-secondary);
  font-size: 48px;
  font-weight: 800;
  fill: var(--primary);
}

.loader-bar {
  width: 200px;
  height: 4px;
  background: var(--border-light);
  border-radius: 2px;
  overflow: hidden;
}

.loader-progress {
  height: 100%;
  background: var(--primary);
  animation: loading 1.5s ease infinite;
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

@keyframes loading {
  0% { width: 0; }
  50% { width: 70%; }
  100% { width: 100%; }
}

/* App Container */
.app {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  opacity: 0;
  animation: fadeIn 0.5s ease forwards;
  animation-delay: 0.3s;
}

@keyframes fadeIn {
  to { opacity: 1; }
}

/* Header */
.header {
  background: var(--bg-primary);
  border-bottom: 1px solid var(--border-light);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow-sm);
}

.header-container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 16px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

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

.brand-text {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.5px;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 20px;
}

/* Progress Indicator */
.progress-indicator {
  display: flex;
  align-items: center;
  gap: 12px;
}

.progress-text {
  font-family: var(--font-secondary);
  font-size: 14px;
  font-weight: 500;
  color: var(--text-secondary);
}

.progress-bar {
  width: 120px;
  height: 6px;
  background: var(--border-light);
  border-radius: 3px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--primary-light));
  transition: width 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

/* View Controls */
.view-controls {
  display: flex;
  gap: 4px;
  background: var(--bg-tertiary);
  padding: 4px;
  border-radius: var(--radius-md);
}

.view-btn {
  padding: 8px;
  background: transparent;
  border: none;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  cursor: pointer;
  transition: var(--transition-fast);
  display: flex;
  align-items: center;
  justify-content: center;
}

.view-btn:hover {
  color: var(--text-secondary);
}

.view-btn.active {
  background: var(--bg-primary);
  color: var(--primary);
  box-shadow: var(--shadow-sm);
}


/* Main Content */
.main {
  flex: 1;
  max-width: 1400px;
  width: 100%;
  margin: 0 auto;
  padding: 32px 24px;
}

/* Card View */
.card-view {
  display: none;
}

.card-view.active {
  display: block;
  animation: slideIn 0.3s ease;
}

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

.card-stage {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 24px;
  min-height: 500px;
  margin-bottom: 32px;
}

/* Navigation Buttons */
.nav-btn {
  width: 48px;
  height: 48px;
  border-radius: 50%;
  background: var(--bg-primary);
  border: 2px solid var(--border-light);
  color: var(--text-secondary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}

.nav-btn:hover:not(:disabled) {
  border-color: var(--primary);
  color: var(--primary);
  transform: scale(1.05);
  box-shadow: var(--shadow-md);
}

.nav-btn:active:not(:disabled) {
  transform: scale(0.95);
}

.nav-btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

/* Flashcard Container */
.flashcard-container {
  perspective: 1000px;
  width: 100%;
  max-width: 600px;
  aspect-ratio: 16 / 10;
}

.flashcard {
  width: 100%;
  height: 100%;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  cursor: pointer;
}

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

.card-front,
.card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  background: var(--bg-primary);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
  display: flex;
  flex-direction: column;
  padding: 32px;
  border: 1px solid var(--border-light);
}

.card-back {
  transform: rotateY(180deg);
}

.card-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: auto;
}

.card-number {
  font-family: var(--font-secondary);
  font-size: 14px;
  font-weight: 600;
  color: var(--primary);
  background: var(--primary-bg);
  padding: 4px 12px;
  border-radius: var(--radius-sm);
}

.card-category {
  font-size: 12px;
  font-weight: 500;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 1px;
}

.card-content {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 24px 16px;
}

.card-title {
  font-size: 28px;
  font-weight: 700;
  line-height: 1.3;
  text-align: center;
  color: var(--text-primary);
}

.card-answer {
  font-size: 18px;
  line-height: 1.7;
  text-align: center;
  color: var(--text-secondary);
  max-width: 100%;
  padding: 0 8px;
}

.card-footer {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 16px;
  margin-top: auto;
}

.card-hint {
  font-size: 12px;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 1px;
}

/* Card Controls */
.card-controls {
  display: flex;
  justify-content: center;
  align-items: center;
  max-width: 600px;
  margin: 0 auto;
  padding: 24px 32px;
  background: linear-gradient(135deg, var(--bg-primary) 0%, var(--bg-secondary) 100%);
  border-radius: var(--radius-xl);
  border: 1px solid var(--border-light);
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.06);
}

.keyboard-hints {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 20px;
  font-size: 14px;
  color: var(--text-secondary);
  font-weight: 500;
}

.keyboard-hints kbd {
  padding: 8px 16px;
  background: var(--bg-primary);
  border: 1.5px solid var(--border-light);
  border-radius: var(--radius-md);
  font-family: var(--font-secondary);
  font-size: 13px;
  font-weight: 600;
  min-width: 40px;
  text-align: center;
  display: inline-block;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.06);
  transition: all 0.2s ease;
  color: var(--text-primary);
  letter-spacing: 0.5px;
}

.keyboard-hints kbd:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08), 0 2px 4px rgba(0, 0, 0, 0.08);
  border-color: var(--primary);
}


/* Grid View */
.grid-view {
  display: none;
}

.grid-view.active {
  display: block;
  animation: slideIn 0.3s ease;
}

.grid-filters {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 24px;
  margin-bottom: 32px;
  flex-wrap: wrap;
}

.filter-group {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

.filter-btn {
  padding: 8px 16px;
  background: var(--bg-primary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  font-size: 14px;
  font-weight: 500;
  color: var(--text-secondary);
  cursor: pointer;
  transition: var(--transition);
}

.filter-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
}

.filter-btn.active {
  background: var(--primary);
  color: var(--text-inverse);
  border-color: var(--primary);
}

.search-box {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 16px;
  background: var(--bg-primary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  min-width: 280px;
}

.search-box:focus-within {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-bg);
}

.search-box svg {
  color: var(--text-muted);
  flex-shrink: 0;
}

.search-box input {
  flex: 1;
  border: none;
  outline: none;
  font-size: 14px;
  color: var(--text-primary);
  background: transparent;
}

.search-box input::placeholder {
  color: var(--text-muted);
}

/* Cards Grid */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 20px;
}

.grid-card {
  background: var(--bg-primary);
  border: 1px solid var(--border-light);
  border-radius: var(--radius-lg);
  padding: 20px;
  cursor: pointer;
  transition: var(--transition);
  position: relative;
  min-height: 180px;
  display: flex;
  flex-direction: column;
}

.grid-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: var(--primary);
}

.grid-card.flipped {
  background: var(--bg-tertiary);
}

.grid-card-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 12px;
}

.grid-card-number {
  font-family: var(--font-secondary);
  font-size: 12px;
  font-weight: 600;
  color: var(--primary);
  background: var(--primary-bg);
  padding: 2px 8px;
  border-radius: var(--radius-sm);
}


.grid-card-content {
  flex: 1;
  display: flex;
  align-items: center;
}

.grid-card-title {
  font-size: 16px;
  font-weight: 600;
  line-height: 1.4;
  color: var(--text-primary);
}

.grid-card-answer {
  font-size: 14px;
  line-height: 1.6;
  color: var(--text-secondary);
  display: none;
}

.grid-card.flipped .grid-card-title {
  display: none;
}

.grid-card.flipped .grid-card-answer {
  display: block;
}

/* Footer */
.footer {
  background: var(--bg-primary);
  border-top: 1px solid var(--border-light);
  margin-top: auto;
}

.footer-container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 24px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
}

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

.footer-links {
  display: flex;
  gap: 24px;
}

.footer-links a {
  font-size: 14px;
  color: var(--text-secondary);
  text-decoration: none;
  transition: var(--transition);
}

.footer-links a:hover {
  color: var(--primary);
}

/* Animations */
.card-transition-left {
  animation: slideLeft 0.3s ease;
}

.card-transition-right {
  animation: slideRight 0.3s ease;
}

@keyframes slideLeft {
  from {
    opacity: 0;
    transform: translateX(30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes slideRight {
  from {
    opacity: 0;
    transform: translateX(-30px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

/* Responsive Design */
@media (max-width: 1024px) {
  .cards-grid {
    grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  }
}

@media (max-width: 768px) {
  .header-container {
    padding: 12px 16px;
    justify-content: center;
  }
  
  .header-nav {
    display: none;
  }
  
  .main {
    padding: 16px 12px;
  }
  
  /* Hide card view on mobile */
  .card-view {
    display: none !important;
  }
  
  /* Hide grid filters on mobile */
  .grid-filters {
    display: none;
  }
  
  /* Grid view always active on mobile */
  .grid-view {
    display: block !important;
  }
  
  .cards-grid {
    grid-template-columns: 1fr;
    gap: 16px;
  }
  
  .footer-container {
    flex-direction: column;
    text-align: center;
  }
  
  .footer-links {
    gap: 16px;
  }
}

@media (max-width: 480px) {
  
  .flashcard-container {
    aspect-ratio: 1 / 1;
  }
  
  .card-title {
    font-size: 18px;
  }
  
  .card-answer {
    font-size: 14px;
    padding: 0 8px;
  }
  
  .card-front,
  .card-back {
    padding: 20px;
  }
}

/* Print Styles */
@media print {
  .header,
  .footer,
  .view-controls,
  .nav-btn,
  .card-controls {
    display: none !important;
  }
  
  .cards-grid {
    display: block !important;
  }
  
  .grid-card {
    page-break-inside: avoid;
    margin-bottom: 20px;
    border: 1px solid #000;
  }
}