/* ============================================================
   Mi English v2.0 — Design System
   Xiaomi International English Academy
   ============================================================ */

/* ---------- Google Fonts ---------- */
@import url('https://fonts.googleapis.com/css2?family=Plus+Jakarta+Sans:wght@400;500;600;700;800&display=swap');

/* ---------- CSS Custom Properties ---------- */
:root {
  /* Brand Colors */
  --mi-orange: #FF6900;
  --mi-orange-light: #FFF3E8;
  --mi-orange-dark: #E55D00;
  --mi-green: #10B981;
  --mi-green-light: #ECFDF5;
  --mi-blue: #3B82F6;
  --mi-blue-light: #EFF6FF;
  --mi-red: #EF4444;
  --mi-red-light: #FEF2F2;
  --mi-yellow: #F59E0B;
  --mi-yellow-light: #FFFBEB;
  --mi-purple: #8B5CF6;

  /* Neutrals — warm tone */
  --bg: #FAFAF8;
  --bg-card: #FFFFFF;
  --bg-hover: #F5F3F0;
  --border: #E8E4DF;
  --border-light: #F0EDE8;
  --text-primary: #1A1A2E;
  --text-secondary: #6B7280;
  --text-muted: #9CA3AF;
  --text-inverse: #FFFFFF;

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.04), 0 1px 2px rgba(0,0,0,0.06);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.06), 0 1px 3px rgba(0,0,0,0.04);
  --shadow-lg: 0 12px 40px rgba(0,0,0,0.08), 0 4px 12px rgba(0,0,0,0.04);
  --shadow-glow: 0 0 20px rgba(255,105,0,0.15);

  /* Radii */
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 20px;
  --radius-full: 9999px;

  /* Transitions */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --duration-fast: 150ms;
  --duration-normal: 250ms;
  --duration-slow: 400ms;
}

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

html {
  -webkit-text-size-adjust: 100%;
  -webkit-tap-highlight-color: transparent;
  scroll-behavior: smooth;
}

body {
  font-family: 'Plus Jakarta Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text-primary);
  line-height: 1.6;
  min-height: 100vh;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

/* ---------- Typography ---------- */
h1, h2, h3, h4 { font-weight: 700; line-height: 1.3; }
h1 { font-size: 1.75rem; letter-spacing: -0.02em; }
h2 { font-size: 1.375rem; letter-spacing: -0.01em; }
h3 { font-size: 1.125rem; }
h4 { font-size: 0.9375rem; }

.text-xs { font-size: 0.75rem; }
.text-sm { font-size: 0.8125rem; }
.text-base { font-size: 0.9375rem; }
.text-lg { font-size: 1.125rem; }
.text-xl { font-size: 1.25rem; }
.text-2xl { font-size: 1.5rem; }
.text-3xl { font-size: 2rem; letter-spacing: -0.02em; }

.font-medium { font-weight: 500; }
.font-semibold { font-weight: 600; }
.font-bold { font-weight: 700; }
.font-extrabold { font-weight: 800; }

/* ---------- Layout ---------- */
.container {
  max-width: 640px;
  margin: 0 auto;
  padding: 0 16px;
}

.page-content {
  padding: 16px 0 100px;
}

/* ---------- Navigation — Top Bar ---------- */
.nav-header {
  background: var(--bg-card);
  border-bottom: 1px solid var(--border-light);
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 16px;
  max-width: 640px;
  margin: 0 auto;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  color: var(--text-primary);
}

.nav-logo {
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  background: var(--mi-orange);
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 800;
  font-size: 13px;
  letter-spacing: -0.5px;
}

.nav-title {
  font-weight: 700;
  font-size: 1.125rem;
}

.nav-subtitle {
  font-size: 0.6875rem;
  color: var(--text-muted);
  margin-left: 4px;
}

.nav-stats {
  font-size: 0.75rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 6px;
}

.nav-streak {
  display: flex;
  align-items: center;
  gap: 3px;
  padding: 3px 8px;
  background: var(--mi-orange-light);
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--mi-orange);
}

/* ---------- Bottom Tab Bar ---------- */
.tab-bar {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  background: var(--bg-card);
  border-top: 1px solid var(--border-light);
  display: flex;
  z-index: 100;
  padding-bottom: env(safe-area-inset-bottom, 0);
}

.tab-bar-btn {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 8px 0 6px;
  font-size: 10px;
  font-weight: 500;
  color: var(--text-muted);
  background: none;
  border: none;
  cursor: pointer;
  transition: color var(--duration-fast);
  text-decoration: none;
  position: relative;
}

.tab-bar-btn.active {
  color: var(--mi-orange);
}

.tab-bar-btn.active::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: 24px;
  height: 2px;
  background: var(--mi-orange);
  border-radius: 0 0 2px 2px;
}

.tab-bar-btn i {
  font-size: 20px;
  margin-bottom: 3px;
}

/* ---------- Cards ---------- */
.card {
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--border-light);
  overflow: hidden;
}

.card-padded {
  padding: 20px;
}

/* ---------- Flashcard — 3D Flip (FIXED) ---------- */
.flashcard-container {
  perspective: 1200px;
  width: 100%;
  max-width: 480px;
  margin: 0 auto;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  transition: transform 0.5s var(--ease-out);
  transform-style: preserve-3d;
  cursor: pointer;
  /* KEY FIX: Use min-height + padding hack for proper height */
  min-height: 240px;
}

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

.flashcard-face {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  border-radius: var(--radius-xl);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 32px 24px;
  text-align: center;
}

.flashcard-front {
  background: var(--bg-card);
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-light);
}

.flashcard-back {
  background: linear-gradient(135deg, var(--mi-orange-light), #FFFAF5);
  box-shadow: var(--shadow-md);
  border: 1px solid rgba(255, 105, 0, 0.15);
  transform: rotateY(180deg);
}

.flashcard-tag {
  position: absolute;
  top: 12px;
  left: 16px;
  font-size: 0.6875rem;
  font-weight: 700;
  padding: 2px 10px;
  border-radius: var(--radius-full);
  background: var(--mi-orange-light);
  color: var(--mi-orange);
}

.flashcard-en {
  font-size: 1.375rem;
  font-weight: 700;
  color: var(--text-primary);
  line-height: 1.4;
  max-width: 100%;
  word-break: break-word;
}

.flashcard-hint {
  font-size: 0.75rem;
  color: var(--text-muted);
  margin-top: 12px;
  display: flex;
  align-items: center;
  gap: 4px;
}

.flashcard-zh {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 8px;
}

.flashcard-scene {
  font-size: 0.8125rem;
  color: var(--text-secondary);
}

.flashcard-example {
  font-size: 0.8125rem;
  color: var(--mi-orange-dark);
  font-style: italic;
  margin-top: 8px;
}

@media (min-width: 640px) {
  .flashcard-inner { min-height: 280px; }
  .flashcard-face { padding: 40px 32px; }
  .flashcard-en { font-size: 1.5rem; }
}

/* ---------- Action Buttons ---------- */
.action-row {
  display: flex;
  gap: 10px;
  justify-content: center;
  margin-top: 20px;
}

.action-btn {
  flex: 1;
  max-width: 120px;
  padding: 10px 0;
  border-radius: var(--radius-md);
  border: none;
  font-size: 0.8125rem;
  font-weight: 600;
  color: white;
  cursor: pointer;
  transition: transform var(--duration-fast) var(--ease-spring), box-shadow var(--duration-fast);
  font-family: inherit;
}

.action-btn:active {
  transform: scale(0.95);
}

.action-btn--green { background: var(--mi-green); }
.action-btn--yellow { background: var(--mi-yellow); }
.action-btn--red { background: var(--mi-red); }

.action-btn:hover {
  box-shadow: 0 4px 12px rgba(0,0,0,0.15);
}

/* ---------- Nav Arrows ---------- */
.nav-arrows {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 24px;
  margin-top: 16px;
}

.nav-arrow {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: var(--bg-hover);
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-secondary);
  transition: all var(--duration-fast);
  font-family: inherit;
}

.nav-arrow:hover {
  background: var(--border);
}

.card-status {
  font-size: 0.8125rem;
  color: var(--text-muted);
}

/* ---------- Filter Bar ---------- */
.filter-bar {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 16px;
  flex-wrap: wrap;
}

.filter-select {
  font-size: 0.8125rem;
  font-family: inherit;
  padding: 6px 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  color: var(--text-primary);
  outline: none;
  cursor: pointer;
  transition: border-color var(--duration-fast);
}

.filter-select:focus {
  border-color: var(--mi-orange);
}

.filter-btn {
  padding: 6px 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-card);
  color: var(--text-secondary);
  cursor: pointer;
  font-size: 0.8125rem;
  font-family: inherit;
  transition: all var(--duration-fast);
}

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

.filter-counter {
  margin-left: auto;
  font-size: 0.8125rem;
  color: var(--text-muted);
}

/* ---------- Practice Mode Tabs ---------- */
.mode-tabs {
  display: flex;
  gap: 6px;
  margin-bottom: 16px;
  background: var(--bg-hover);
  border-radius: var(--radius-md);
  padding: 4px;
}

.mode-tab {
  flex: 1;
  padding: 8px 0;
  border-radius: var(--radius-sm);
  border: none;
  font-size: 0.8125rem;
  font-weight: 600;
  font-family: inherit;
  color: var(--text-secondary);
  background: transparent;
  cursor: pointer;
  transition: all var(--duration-fast);
}

.mode-tab.active {
  background: var(--bg-card);
  color: var(--mi-orange);
  box-shadow: var(--shadow-sm);
}

/* ---------- Match Game ---------- */
.match-item {
  padding: 12px 16px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border);
  background: var(--bg-card);
  cursor: pointer;
  user-select: none;
  font-size: 0.875rem;
  transition: all var(--duration-fast);
}

.match-item:hover { border-color: var(--mi-orange); }

.match-item.selected {
  border-color: var(--mi-orange);
  box-shadow: 0 0 0 2px rgba(255,105,0,0.2);
  transform: scale(1.02);
}

.match-item.correct {
  background: var(--mi-green-light) !important;
  border-color: var(--mi-green) !important;
}

.match-item.wrong {
  animation: shake 0.4s var(--ease-out);
}

.match-item-zh {
  background: var(--mi-blue-light);
  border-color: rgba(59,130,246,0.2);
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-6px); }
  75% { transform: translateX(6px); }
}

/* ---------- Progress Bars ---------- */
.progress-track {
  height: 8px;
  border-radius: 4px;
  background: var(--border-light);
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  border-radius: 4px;
  transition: width 0.6s var(--ease-out);
}

.progress-fill--orange { background: var(--mi-orange); }
.progress-fill--green { background: var(--mi-green); }
.progress-fill--blue { background: var(--mi-blue); }

/* ---------- Stats Grid ---------- */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  margin-bottom: 20px;
}

.stat-card {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 12px 8px;
  text-align: center;
  border: 1px solid var(--border-light);
}

.stat-icon { font-size: 1.25rem; margin-bottom: 4px; }
.stat-value { font-size: 1.125rem; font-weight: 700; }
.stat-label { font-size: 0.6875rem; color: var(--text-muted); margin-top: 2px; }

/* ---------- Level Badge ---------- */
.level-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  border-radius: var(--radius-full);
  background: linear-gradient(135deg, var(--mi-orange), var(--mi-orange-dark));
  color: white;
  font-size: 0.75rem;
  font-weight: 700;
}

/* ---------- Achievement Grid ---------- */
.achievement-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: 10px;
}

.achievement-item {
  background: var(--bg-card);
  border-radius: var(--radius-md);
  padding: 16px 12px;
  text-align: center;
  border: 1px solid var(--border-light);
  transition: all var(--duration-normal);
}

.achievement-item.locked {
  opacity: 0.4;
  filter: grayscale(1);
}

.achievement-item.unlocked {
  border-color: var(--mi-orange);
  box-shadow: var(--shadow-glow);
}

.achievement-icon {
  font-size: 2rem;
  margin-bottom: 6px;
}

.achievement-title {
  font-size: 0.8125rem;
  font-weight: 700;
  margin-bottom: 2px;
}

.achievement-desc {
  font-size: 0.6875rem;
  color: var(--text-muted);
}

.achievement-date {
  font-size: 0.625rem;
  color: var(--mi-orange);
  margin-top: 4px;
}

/* ---------- Accordion ---------- */
.accordion {
  margin-bottom: 10px;
}

.accordion-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 16px;
  background: var(--bg-card);
  border-radius: var(--radius-md);
  border: 1px solid var(--border-light);
  cursor: pointer;
  user-select: none;
  transition: all var(--duration-fast);
}

.accordion-header:hover {
  border-color: var(--border);
}

.accordion-body {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.3s var(--ease-out);
}

.accordion-body.open {
  max-height: 8000px;
}

.accordion-content {
  padding: 0 16px 16px;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-top: none;
  border-radius: 0 0 var(--radius-md) var(--radius-md);
}

/* ---------- Search ---------- */
.search-box {
  position: relative;
  margin-bottom: 16px;
}

.search-box i {
  position: absolute;
  left: 14px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  font-size: 0.875rem;
}

.search-input {
  width: 100%;
  padding: 10px 16px 10px 40px;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background: var(--bg-card);
  font-size: 0.875rem;
  font-family: inherit;
  outline: none;
  transition: border-color var(--duration-fast);
}

.search-input:focus {
  border-color: var(--mi-orange);
}

/* ---------- Vocab Table ---------- */
.vocab-table {
  width: 100%;
  font-size: 0.8125rem;
  border-collapse: collapse;
}

.vocab-table th {
  text-align: left;
  font-size: 0.6875rem;
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 6px 0;
}

.vocab-table td {
  padding: 8px 8px 8px 0;
  border-top: 1px solid var(--border-light);
  vertical-align: top;
}

.vocab-table .en { font-weight: 600; color: var(--text-primary); }
.vocab-table .zh { color: var(--text-secondary); }
.vocab-table .scene { color: var(--text-muted); font-size: 0.75rem; }

/* ---------- Lesson Tag ---------- */
.lesson-tag {
  display: inline-block;
  font-size: 0.6875rem;
  font-weight: 700;
  padding: 2px 10px;
  border-radius: var(--radius-full);
  background: var(--mi-orange);
  color: white;
}

/* ---------- Toast / Notification ---------- */
.toast {
  position: fixed;
  top: 80px;
  left: 50%;
  transform: translateX(-50%) translateY(-20px);
  background: var(--text-primary);
  color: white;
  padding: 12px 24px;
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 600;
  z-index: 200;
  opacity: 0;
  pointer-events: none;
  transition: all var(--duration-normal) var(--ease-out);
  box-shadow: var(--shadow-lg);
}

.toast.show {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

.toast.achievement {
  background: linear-gradient(135deg, var(--mi-orange), #FF8533);
}

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 10px 20px;
  border-radius: var(--radius-md);
  border: none;
  font-size: 0.875rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: all var(--duration-fast);
}

.btn-primary {
  background: var(--mi-orange);
  color: white;
}
.btn-primary:hover { background: var(--mi-orange-dark); }

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

.btn-danger {
  background: transparent;
  border: 1px solid var(--mi-red);
  color: var(--mi-red);
}
.btn-danger:hover { background: var(--mi-red-light); }

.btn-block { width: 100%; }

/* ---------- Data Management Section ---------- */
.data-actions {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin-top: 16px;
}

/* ---------- Section Headers ---------- */
.section-title {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 12px;
}

.section-title i {
  color: var(--mi-orange);
}

/* ---------- Empty State ---------- */
.empty-state {
  text-align: center;
  padding: 40px 20px;
  color: var(--text-muted);
}

.empty-state i {
  font-size: 2.5rem;
  margin-bottom: 12px;
  opacity: 0.4;
}

/* ---------- Animations ---------- */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes scaleIn {
  from { opacity: 0; transform: scale(0.9); }
  to { opacity: 1; transform: scale(1); }
}

@keyframes slideUp {
  from { opacity: 0; transform: translateY(16px); }
  to { opacity: 1; transform: translateY(0); }
}

.animate-fadeIn { animation: fadeIn 0.4s var(--ease-out) both; }
.animate-scaleIn { animation: scaleIn 0.3s var(--ease-spring) both; }
.animate-slideUp { animation: slideUp 0.5s var(--ease-out) both; }

.delay-1 { animation-delay: 0.05s; }
.delay-2 { animation-delay: 0.1s; }
.delay-3 { animation-delay: 0.15s; }
.delay-4 { animation-delay: 0.2s; }

/* ---------- Scrollbar ---------- */
::-webkit-scrollbar { width: 4px; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 2px; }

/* ---------- Responsive ---------- */
@media (max-width: 380px) {
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .achievement-grid { grid-template-columns: repeat(2, 1fr); }
}

/* ---------- Utility ---------- */
.text-orange { color: var(--mi-orange); }
.text-green { color: var(--mi-green); }
.text-red { color: var(--mi-red); }
.text-yellow { color: var(--mi-yellow); }
.text-muted { color: var(--text-muted); }
.text-center { text-align: center; }
.mt-2 { margin-top: 8px; }
.mt-3 { margin-top: 12px; }
.mt-4 { margin-top: 16px; }
.mt-6 { margin-top: 24px; }
.mb-2 { margin-bottom: 8px; }
.mb-3 { margin-bottom: 12px; }
.mb-4 { margin-bottom: 16px; }
.mb-6 { margin-bottom: 24px; }
.gap-2 { gap: 8px; }
.gap-3 { gap: 12px; }
.hidden { display: none !important; }