/* ============================================================
   JLPT N5 Learning Website - Design System
   Version: 1.0
   Style: Japanese Minimalist Aesthetic (Wabi-Sabi inspired)
   ============================================================ */

/* ----------------------------------------
   0. Google Fonts Import
   ---------------------------------------- */
@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+JP:wght@300;400;500;600;700&family=Noto+Serif+JP:wght@400;500;600;700&family=Inter:wght@300;400;500;600;700&display=swap');

/* ----------------------------------------
   1. CSS Custom Properties (Design Tokens)
   ---------------------------------------- */
:root {
  /* --- Color Palette: Light Mode --- */

  /* Primary: Deep Indigo (Ai-iro, Japanese indigo) */
  --color-primary-50:  #eef2ff;
  --color-primary-100: #dce4ff;
  --color-primary-200: #b9c9ff;
  --color-primary-300: #8da6ff;
  --color-primary-400: #6182fc;
  --color-primary-500: #4361ee;
  --color-primary-600: #3347d1;
  --color-primary-700: #2a38a8;
  --color-primary-800: #263189;
  --color-primary-900: #1e2a6e;

  /* Secondary: Sakura Pink */
  --color-secondary-50:  #fff1f3;
  --color-secondary-100: #ffe0e6;
  --color-secondary-200: #ffc7d2;
  --color-secondary-300: #ffa1b4;
  --color-secondary-400: #ff6b8a;
  --color-secondary-500: #f43f63;
  --color-secondary-600: #d91e4a;
  --color-secondary-700: #b8133d;
  --color-secondary-800: #9a1339;
  --color-secondary-900: #841436;

  /* Accent: Warm Gold (Kinsui, golden water) */
  --color-accent-50:  #fffbeb;
  --color-accent-100: #fff3c6;
  --color-accent-200: #ffe588;
  --color-accent-300: #ffd24a;
  --color-accent-400: #ffbf20;
  --color-accent-500: #f59e07;
  --color-accent-600: #d97602;
  --color-accent-700: #b45106;
  --color-accent-800: #923e0c;
  --color-accent-900: #78330d;

  /* Neutral: Warm Gray (Nezumi-iro) */
  --color-neutral-0:   #ffffff;
  --color-neutral-50:  #f9fafb;
  --color-neutral-100: #f3f4f6;
  --color-neutral-200: #e5e7eb;
  --color-neutral-300: #d1d5db;
  --color-neutral-400: #9ca3af;
  --color-neutral-500: #6b7280;
  --color-neutral-600: #4b5563;
  --color-neutral-700: #374151;
  --color-neutral-800: #1f2937;
  --color-neutral-900: #111827;
  --color-neutral-950: #030712;

  /* Semantic Colors */
  --color-success-50:  #ecfdf5;
  --color-success-100: #d1fae5;
  --color-success-200: #a7f3d0;
  --color-success-400: #34d399;
  --color-success-500: #10b981;
  --color-success-600: #059669;
  --color-success-700: #047857;

  --color-error-50:  #fef2f2;
  --color-error-100: #fee2e2;
  --color-error-200: #fecaca;
  --color-error-400: #f87171;
  --color-error-500: #ef4444;
  --color-error-600: #dc2626;
  --color-error-700: #b91c1c;

  --color-warning-50:  #fffbeb;
  --color-warning-100: #fef3c7;
  --color-warning-400: #fbbf24;
  --color-warning-500: #f59e0b;
  --color-warning-600: #d97706;

  --color-info-50:  #eff6ff;
  --color-info-100: #dbeafe;
  --color-info-400: #60a5fa;
  --color-info-500: #3b82f6;
  --color-info-600: #2563eb;

  /* --- Semantic Aliases --- */
  --bg-primary:    var(--color-neutral-0);
  --bg-secondary:  var(--color-neutral-50);
  --bg-tertiary:   var(--color-neutral-100);
  --bg-elevated:   var(--color-neutral-0);

  --text-primary:   var(--color-neutral-900);
  --text-secondary: var(--color-neutral-600);
  --text-tertiary:  var(--color-neutral-400);
  --text-inverse:   var(--color-neutral-0);

  --border-default: var(--color-neutral-200);
  --border-strong:  var(--color-neutral-300);

  /* --- Typography --- */
  --font-sans-jp: 'Noto Sans JP', 'Hiragino Sans', 'Hiragino Kaku Gothic ProN', 'Meiryo', sans-serif;
  --font-serif-jp: 'Noto Serif JP', 'Hiragino Mincho ProN', 'Yu Mincho', serif;
  --font-sans-en: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'Fira Code', 'Consolas', monospace;

  --font-body: var(--font-sans-jp);
  --font-heading: var(--font-sans-jp);

  /* Font Sizes (modular scale ~1.25) */
  --text-xs:   0.75rem;    /* 12px */
  --text-sm:   0.875rem;   /* 14px */
  --text-base: 1rem;       /* 16px */
  --text-lg:   1.125rem;   /* 18px */
  --text-xl:   1.25rem;    /* 20px */
  --text-2xl:  1.5rem;     /* 24px */
  --text-3xl:  1.875rem;   /* 30px */
  --text-4xl:  2.25rem;    /* 36px */
  --text-5xl:  3rem;       /* 48px */

  /* Font Weights */
  --font-light:    300;
  --font-regular:  400;
  --font-medium:   500;
  --font-semibold: 600;
  --font-bold:     700;

  /* Line Heights */
  --leading-tight:  1.25;
  --leading-snug:   1.375;
  --leading-normal: 1.625;
  --leading-relaxed: 1.75;
  --leading-loose:  2;

  /* Letter Spacing */
  --tracking-tight:  -0.025em;
  --tracking-normal:  0;
  --tracking-wide:    0.025em;
  --tracking-wider:   0.05em;
  --tracking-widest:  0.1em;

  /* --- Spacing (8px base) --- */
  --space-0:   0;
  --space-0-5: 0.125rem;  /* 2px */
  --space-1:   0.25rem;   /* 4px */
  --space-1-5: 0.375rem;  /* 6px */
  --space-2:   0.5rem;    /* 8px */
  --space-3:   0.75rem;   /* 12px */
  --space-4:   1rem;      /* 16px */
  --space-5:   1.25rem;   /* 20px */
  --space-6:   1.5rem;    /* 24px */
  --space-8:   2rem;      /* 32px */
  --space-10:  2.5rem;    /* 40px */
  --space-12:  3rem;      /* 48px */
  --space-16:  4rem;      /* 64px */
  --space-20:  5rem;      /* 80px */
  --space-24:  6rem;      /* 96px */

  /* --- Border Radius --- */
  --radius-sm:   0.25rem;   /* 4px */
  --radius-md:   0.5rem;    /* 8px */
  --radius-lg:   0.75rem;   /* 12px */
  --radius-xl:   1rem;      /* 16px */
  --radius-2xl:  1.5rem;    /* 24px */
  --radius-full: 9999px;

  /* --- Shadows --- */
  --shadow-xs:  0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-sm:  0 1px 3px 0 rgba(0, 0, 0, 0.08), 0 1px 2px -1px rgba(0, 0, 0, 0.08);
  --shadow-md:  0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -2px rgba(0, 0, 0, 0.08);
  --shadow-lg:  0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.08);
  --shadow-xl:  0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.08);
  --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.2);

  /* --- Transitions --- */
  --duration-fast:    150ms;
  --duration-normal:  250ms;
  --duration-slow:    350ms;
  --duration-slower:  500ms;
  --ease-default: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-in:      cubic-bezier(0.4, 0, 1, 1);
  --ease-out:     cubic-bezier(0, 0, 0.2, 1);
  --ease-in-out:  cubic-bezier(0.4, 0, 0.2, 1);
  --ease-bounce:  cubic-bezier(0.34, 1.56, 0.64, 1);

  /* --- Layout --- */
  --container-sm:  640px;
  --container-md:  768px;
  --container-lg:  1024px;
  --container-xl:  1200px;
  --container-2xl: 1400px;

  /* --- Z-Index Scale --- */
  --z-dropdown:  1000;
  --z-sticky:    1020;
  --z-fixed:     1030;
  --z-modal-backdrop: 1040;
  --z-modal:     1050;
  --z-popover:   1060;
  --z-tooltip:   1070;
  --z-toast:     1080;
}

/* ----------------------------------------
   Dark Mode Color Overrides
   ---------------------------------------- */
[data-theme="dark"] {
  --bg-primary:    #0f1119;
  --bg-secondary:  #171923;
  --bg-tertiary:   #1e2130;
  --bg-elevated:   #232638;

  --text-primary:   #e8eaf0;
  --text-secondary: #a0a6b8;
  --text-tertiary:  #636b82;
  --text-inverse:   #0f1119;

  --border-default: #2a2e3f;
  --border-strong:  #3a3f54;

  --color-primary-50:  #1a1e35;
  --color-primary-100: #232951;
  --color-primary-200: #2e3872;
  --color-primary-500: #6182fc;
  --color-primary-600: #7b99ff;

  --color-secondary-50:  #2a1520;
  --color-secondary-100: #3d1a2e;
  --color-secondary-500: #ff6b8a;

  --color-accent-50:  #2a2010;
  --color-accent-100: #3d3015;
  --color-accent-500: #ffd24a;

  --shadow-xs:  0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-sm:  0 1px 3px 0 rgba(0, 0, 0, 0.4), 0 1px 2px -1px rgba(0, 0, 0, 0.4);
  --shadow-md:  0 4px 6px -1px rgba(0, 0, 0, 0.4), 0 2px 4px -2px rgba(0, 0, 0, 0.4);
  --shadow-lg:  0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -4px rgba(0, 0, 0, 0.4);
  --shadow-xl:  0 20px 25px -5px rgba(0, 0, 0, 0.5), 0 8px 10px -6px rgba(0, 0, 0, 0.4);
  --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.6);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: var(--text-base);
  font-weight: var(--font-regular);
  line-height: var(--leading-normal);
  color: var(--text-primary);
  background-color: var(--bg-primary);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  transition: background-color var(--duration-slow) var(--ease-default),
              color var(--duration-slow) var(--ease-default);
}

img, svg {
  display: block;
  max-width: 100%;
}

button, input, select, textarea {
  font: inherit;
  color: inherit;
}

a {
  color: var(--color-primary-500);
  text-decoration: none;
  transition: color var(--duration-fast) var(--ease-default);
}

a:hover {
  color: var(--color-primary-600);
}

/* ----------------------------------------
   3. Typography
   ---------------------------------------- */
.text-xs   { font-size: var(--text-xs); }
.text-sm   { font-size: var(--text-sm); }
.text-base { font-size: var(--text-base); }
.text-lg   { font-size: var(--text-lg); }
.text-xl   { font-size: var(--text-xl); }
.text-2xl  { font-size: var(--text-2xl); }
.text-3xl  { font-size: var(--text-3xl); }
.text-4xl  { font-size: var(--text-4xl); }
.text-5xl  { font-size: var(--text-5xl); }

h1, .h1 {
  font-family: var(--font-heading);
  font-size: var(--text-4xl);
  font-weight: var(--font-bold);
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
}

h2, .h2 {
  font-family: var(--font-heading);
  font-size: var(--text-3xl);
  font-weight: var(--font-semibold);
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
}

h3, .h3 {
  font-family: var(--font-heading);
  font-size: var(--text-2xl);
  font-weight: var(--font-semibold);
  line-height: var(--leading-snug);
}

h4, .h4 {
  font-family: var(--font-heading);
  font-size: var(--text-xl);
  font-weight: var(--font-medium);
  line-height: var(--leading-snug);
}

h5, .h5 {
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: var(--font-medium);
  line-height: var(--leading-snug);
}

h6, .h6 {
  font-family: var(--font-heading);
  font-size: var(--text-base);
  font-weight: var(--font-semibold);
  line-height: var(--leading-normal);
  text-transform: uppercase;
  letter-spacing: var(--tracking-wider);
}

/* Furigana / Ruby annotation styling */
ruby {
  ruby-align: center;
}

ruby rt {
  font-size: 0.5em;
  font-weight: var(--font-regular);
  color: var(--text-secondary);
}

/* Japanese text helpers */
.text-jp {
  font-family: var(--font-sans-jp);
  line-height: var(--leading-relaxed);
}

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

.text-jp-large {
  font-size: var(--text-3xl);
  font-weight: var(--font-medium);
  letter-spacing: var(--tracking-wide);
}

/* ----------------------------------------
   4. Layout System
   ---------------------------------------- */
.container {
  width: 100%;
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--space-4);
}

@media (min-width: 768px) {
  .container {
    padding-inline: var(--space-6);
  }
}

@media (min-width: 1024px) {
  .container {
    padding-inline: var(--space-8);
  }
}

.container-sm { max-width: var(--container-sm); }
.container-md { max-width: var(--container-md); }
.container-lg { max-width: var(--container-lg); }

/* Grid System */
.grid {
  display: grid;
  gap: var(--space-4);
}

.grid-cols-1 { grid-template-columns: 1fr; }
.grid-cols-2 { grid-template-columns: repeat(2, 1fr); }
.grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
.grid-cols-4 { grid-template-columns: repeat(4, 1fr); }

@media (min-width: 768px) {
  .md\:grid-cols-2 { grid-template-columns: repeat(2, 1fr); }
  .md\:grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
  .md\:grid-cols-4 { grid-template-columns: repeat(4, 1fr); }
}

@media (min-width: 1024px) {
  .lg\:grid-cols-2 { grid-template-columns: repeat(2, 1fr); }
  .lg\:grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
  .lg\:grid-cols-4 { grid-template-columns: repeat(4, 1fr); }
}

/* Flex Utilities */
.flex { display: flex; }
.flex-col { flex-direction: column; }
.flex-wrap { flex-wrap: wrap; }
.items-center { align-items: center; }
.items-start { align-items: flex-start; }
.items-end { align-items: flex-end; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.justify-end { justify-content: flex-end; }
.gap-1 { gap: var(--space-1); }
.gap-2 { gap: var(--space-2); }
.gap-3 { gap: var(--space-3); }
.gap-4 { gap: var(--space-4); }
.gap-6 { gap: var(--space-6); }
.gap-8 { gap: var(--space-8); }

/* Section spacing */
.section {
  padding-block: var(--space-12);
}

@media (min-width: 768px) {
  .section {
    padding-block: var(--space-16);
  }
}

/* ----------------------------------------
   5. Navigation
   ---------------------------------------- */
.navbar {
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-3) var(--space-4);
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-default);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  background-color: color-mix(in srgb, var(--bg-primary) 85%, transparent);
  transition: background-color var(--duration-slow) var(--ease-default);
}

@media (min-width: 768px) {
  .navbar {
    padding: var(--space-3) var(--space-6);
  }
}

.navbar-brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-family: var(--font-heading);
  font-size: var(--text-xl);
  font-weight: var(--font-bold);
  color: var(--text-primary);
  text-decoration: none;
}

.navbar-brand .brand-icon {
  font-size: var(--text-2xl);
}

.navbar-nav {
  display: none;
  list-style: none;
  gap: var(--space-1);
}

@media (min-width: 768px) {
  .navbar-nav {
    display: flex;
  }
}

.navbar-nav .nav-link {
  display: inline-flex;
  align-items: center;
  padding: var(--space-2) var(--space-3);
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-default);
}

.navbar-nav .nav-link:hover {
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
}

.navbar-nav .nav-link.active {
  color: var(--color-primary-600);
  background-color: var(--color-primary-50);
}

[data-theme="dark"] .navbar-nav .nav-link.active {
  color: var(--color-primary-500);
  background-color: var(--color-primary-50);
}

/* Tab Navigation */
.tab-nav {
  display: flex;
  gap: var(--space-1);
  padding: var(--space-1);
  background-color: var(--bg-tertiary);
  border-radius: var(--radius-lg);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

.tab-nav::-webkit-scrollbar {
  display: none;
}

.tab-link {
  flex-shrink: 0;
  display: inline-flex;
  align-items: center;
  gap: var(--space-1-5);
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--text-secondary);
  background: none;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
  white-space: nowrap;
}

.tab-link:hover {
  color: var(--text-primary);
}

.tab-link.active {
  color: var(--text-primary);
  background-color: var(--bg-primary);
  box-shadow: var(--shadow-sm);
}

/* Mobile Hamburger */
.hamburger {
  display: flex;
  flex-direction: column;
  gap: 5px;
  padding: var(--space-2);
  background: none;
  border: none;
  cursor: pointer;
}

@media (min-width: 768px) {
  .hamburger {
    display: none;
  }
}

.hamburger span {
  display: block;
  width: 22px;
  height: 2px;
  background-color: var(--text-primary);
  border-radius: var(--radius-full);
  transition: all var(--duration-normal) var(--ease-default);
}

.hamburger.open span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}

.hamburger.open span:nth-child(2) {
  opacity: 0;
}

.hamburger.open span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

/* Mobile Menu */
.mobile-menu {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: var(--z-modal);
  background-color: var(--bg-primary);
  padding: var(--space-16) var(--space-4) var(--space-4);
  animation: fadeSlideDown var(--duration-normal) var(--ease-out);
}

.mobile-menu.open {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.mobile-menu .nav-link {
  display: block;
  padding: var(--space-3) var(--space-4);
  font-size: var(--text-lg);
  font-weight: var(--font-medium);
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-default);
}

.mobile-menu .nav-link:hover,
.mobile-menu .nav-link.active {
  color: var(--color-primary-600);
  background-color: var(--color-primary-50);
}

/* ----------------------------------------
   6. Buttons
   ---------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-2-5, 0.625rem) var(--space-5);
  font-family: var(--font-body);
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  line-height: 1.5;
  text-decoration: none;
  border: 2px solid transparent;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
  user-select: none;
  -webkit-user-select: none;
  position: relative;
  overflow: hidden;
}

.btn:focus-visible {
  outline: 2px solid var(--color-primary-500);
  outline-offset: 2px;
}

.btn:active {
  transform: scale(0.97);
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

/* Ripple Effect */
.btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: radial-gradient(circle, rgba(255,255,255,0.3) 10%, transparent 10.01%);
  transform: scale(10);
  opacity: 0;
  transition: transform 0.5s, opacity 0.8s;
}

.btn:active::after {
  transform: scale(0);
  opacity: 1;
  transition: 0s;
}

/* Button Variants */
.btn-primary {
  color: white;
  background-color: var(--color-primary-500);
  border-color: var(--color-primary-500);
}

.btn-primary:hover {
  background-color: var(--color-primary-600);
  border-color: var(--color-primary-600);
  box-shadow: 0 4px 14px rgba(67, 97, 238, 0.35);
}

.btn-secondary {
  color: var(--color-primary-600);
  background-color: var(--color-primary-50);
  border-color: var(--color-primary-50);
}

.btn-secondary:hover {
  background-color: var(--color-primary-100);
  border-color: var(--color-primary-100);
}

[data-theme="dark"] .btn-secondary {
  color: var(--color-primary-500);
}

.btn-outline {
  color: var(--text-primary);
  background-color: transparent;
  border-color: var(--border-strong);
}

.btn-outline:hover {
  background-color: var(--bg-tertiary);
  border-color: var(--text-tertiary);
}

.btn-ghost {
  color: var(--text-secondary);
  background-color: transparent;
  border-color: transparent;
}

.btn-ghost:hover {
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
}

.btn-success {
  color: white;
  background-color: var(--color-success-500);
  border-color: var(--color-success-500);
}

.btn-success:hover {
  background-color: var(--color-success-600);
  border-color: var(--color-success-600);
  box-shadow: 0 4px 14px rgba(16, 185, 129, 0.35);
}

.btn-error {
  color: white;
  background-color: var(--color-error-500);
  border-color: var(--color-error-500);
}

.btn-error:hover {
  background-color: var(--color-error-600);
  border-color: var(--color-error-600);
  box-shadow: 0 4px 14px rgba(239, 68, 68, 0.35);
}

.btn-sakura {
  color: white;
  background: linear-gradient(135deg, var(--color-secondary-400), var(--color-secondary-500));
  border-color: transparent;
}

.btn-sakura:hover {
  background: linear-gradient(135deg, var(--color-secondary-500), var(--color-secondary-600));
  box-shadow: 0 4px 14px rgba(244, 63, 99, 0.35);
}

/* Button Sizes */
.btn-sm {
  padding: var(--space-1-5) var(--space-3);
  font-size: var(--text-xs);
  border-radius: var(--radius-sm);
}

.btn-lg {
  padding: var(--space-3) var(--space-6);
  font-size: var(--text-base);
  border-radius: var(--radius-lg);
}

.btn-xl {
  padding: var(--space-4) var(--space-8);
  font-size: var(--text-lg);
  border-radius: var(--radius-lg);
}

.btn-icon {
  padding: var(--space-2);
  border-radius: var(--radius-md);
}

.btn-icon.btn-sm { padding: var(--space-1-5); }
.btn-icon.btn-lg { padding: var(--space-3); }

.btn-full { width: 100%; }

/* ----------------------------------------
   7. Cards
   ---------------------------------------- */
.card {
  position: relative;
  display: flex;
  flex-direction: column;
  background-color: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-xl);
  overflow: hidden;
  transition: all var(--duration-normal) var(--ease-default);
}

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

.card-body {
  padding: var(--space-5);
  flex: 1;
}

.card-header {
  padding: var(--space-4) var(--space-5);
  border-bottom: 1px solid var(--border-default);
}

.card-footer {
  padding: var(--space-3) var(--space-5);
  border-top: 1px solid var(--border-default);
  background-color: var(--bg-secondary);
}

/* Vocabulary Card */
.vocab-card {
  text-align: center;
  padding: var(--space-6);
}

.vocab-card .kanji {
  font-family: var(--font-serif-jp);
  font-size: var(--text-4xl);
  font-weight: var(--font-medium);
  color: var(--text-primary);
  margin-bottom: var(--space-2);
}

.vocab-card .reading {
  font-size: var(--text-lg);
  color: var(--color-primary-500);
  margin-bottom: var(--space-2);
}

.vocab-card .meaning {
  font-size: var(--text-base);
  color: var(--text-secondary);
}

.vocab-card .example {
  margin-top: var(--space-4);
  padding-top: var(--space-4);
  border-top: 1px solid var(--border-default);
  font-size: var(--text-sm);
  color: var(--text-secondary);
  text-align: left;
}

/* ----------------------------------------
   8. Flashcard (3D Flip)
   ---------------------------------------- */
.flashcard-container {
  perspective: 1200px;
  width: 100%;
  max-width: 400px;
  height: 280px;
  margin: 0 auto;
}

.flashcard {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
  transition: transform 0.6s var(--ease-default);
  cursor: pointer;
}

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

.flashcard-face {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: var(--space-6);
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  border-radius: var(--radius-xl);
  border: 1px solid var(--border-default);
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}

.flashcard-front {
  background: linear-gradient(145deg, var(--bg-elevated), var(--bg-secondary));
}

.flashcard-front::before {
  content: '';
  position: absolute;
  top: 0;
  right: 0;
  width: 120px;
  height: 120px;
  background: radial-gradient(circle at top right, var(--color-primary-50), transparent 70%);
  border-radius: 0 var(--radius-xl) 0 0;
}

.flashcard-back {
  background: linear-gradient(145deg, var(--color-primary-500), var(--color-primary-700));
  color: white;
  transform: rotateY(180deg);
}

.flashcard-front .kanji {
  font-family: var(--font-serif-jp);
  font-size: var(--text-5xl);
  font-weight: var(--font-medium);
  margin-bottom: var(--space-3);
  position: relative;
  z-index: 1;
}

.flashcard-front .reading {
  font-size: var(--text-xl);
  color: var(--text-secondary);
  position: relative;
  z-index: 1;
}

.flashcard-front .hint {
  position: absolute;
  bottom: var(--space-4);
  font-size: var(--text-xs);
  color: var(--text-tertiary);
}

.flashcard-back .meaning {
  font-size: var(--text-2xl);
  font-weight: var(--font-semibold);
  margin-bottom: var(--space-3);
}

.flashcard-back .example-sentence {
  font-size: var(--text-sm);
  opacity: 0.85;
  text-align: center;
  line-height: var(--leading-relaxed);
}

/* ----------------------------------------
   9. Progress Bar
   ---------------------------------------- */
.progress {
  width: 100%;
  height: 8px;
  background-color: var(--bg-tertiary);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary-400), var(--color-primary-600));
  border-radius: var(--radius-full);
  transition: width 0.8s var(--ease-out);
  position: relative;
}

.progress-bar::after {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: linear-gradient(
    90deg,
    transparent 0%,
    rgba(255, 255, 255, 0.2) 50%,
    transparent 100%
  );
  animation: progressShimmer 2s ease-in-out infinite;
}

@keyframes progressShimmer {
  0%   { transform: translateX(-100%); }
  100% { transform: translateX(100%); }
}

.progress-lg {
  height: 12px;
}

.progress-sm {
  height: 4px;
}

/* Progress with label */
.progress-labeled {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.progress-label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: var(--text-sm);
}

.progress-label .label-text {
  color: var(--text-secondary);
  font-weight: var(--font-medium);
}

.progress-label .label-value {
  color: var(--text-primary);
  font-weight: var(--font-semibold);
}

/* Circular Progress */
.progress-circle {
  position: relative;
  width: 120px;
  height: 120px;
}

.progress-circle svg {
  transform: rotate(-90deg);
}

.progress-circle .track {
  fill: none;
  stroke: var(--bg-tertiary);
  stroke-width: 8;
}

.progress-circle .fill {
  fill: none;
  stroke: var(--color-primary-500);
  stroke-width: 8;
  stroke-linecap: round;
  transition: stroke-dashoffset 1s var(--ease-out);
}

.progress-circle .value {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--text-xl);
  font-weight: var(--font-bold);
  color: var(--text-primary);
}

/* ----------------------------------------
   10. Quiz Components
   ---------------------------------------- */
.quiz-question {
  margin-bottom: var(--space-6);
}

.quiz-question .question-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  font-size: var(--text-sm);
  font-weight: var(--font-bold);
  color: white;
  background-color: var(--color-primary-500);
  border-radius: var(--radius-full);
  margin-right: var(--space-2);
}

.quiz-question .question-text {
  font-size: var(--text-lg);
  font-weight: var(--font-medium);
  line-height: var(--leading-relaxed);
}

.quiz-question .question-text .highlight {
  text-decoration: underline;
  text-decoration-color: var(--color-primary-300);
  text-decoration-thickness: 2px;
  text-underline-offset: 4px;
}

/* Quiz Options */
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.quiz-option {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-3) var(--space-4);
  background-color: var(--bg-elevated);
  border: 2px solid var(--border-default);
  border-radius: var(--radius-lg);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
  user-select: none;
  -webkit-user-select: none;
}

.quiz-option:hover {
  border-color: var(--color-primary-300);
  background-color: var(--color-primary-50);
}

.quiz-option .option-marker {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  flex-shrink: 0;
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  color: var(--text-secondary);
  background-color: var(--bg-tertiary);
  border-radius: var(--radius-full);
  transition: all var(--duration-fast) var(--ease-default);
}

.quiz-option:hover .option-marker {
  color: var(--color-primary-600);
  background-color: var(--color-primary-100);
}

.quiz-option .option-text {
  font-size: var(--text-base);
  font-family: var(--font-sans-jp);
}

/* Selected State */
.quiz-option.selected {
  border-color: var(--color-primary-500);
  background-color: var(--color-primary-50);
}

.quiz-option.selected .option-marker {
  color: white;
  background-color: var(--color-primary-500);
}

/* Correct State */
.quiz-option.correct {
  border-color: var(--color-success-500);
  background-color: var(--color-success-50);
  animation: correctPulse 0.6s var(--ease-out);
}

.quiz-option.correct .option-marker {
  color: white;
  background-color: var(--color-success-500);
}

/* Incorrect State */
.quiz-option.incorrect {
  border-color: var(--color-error-500);
  background-color: var(--color-error-50);
  animation: shake 0.5s var(--ease-default);
}

.quiz-option.incorrect .option-marker {
  color: white;
  background-color: var(--color-error-500);
}

/* ----------------------------------------
   11. Badges / Tags
   ---------------------------------------- */
.badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-0-5) var(--space-2);
  font-size: var(--text-xs);
  font-weight: var(--font-semibold);
  line-height: 1.5;
  border-radius: var(--radius-full);
  white-space: nowrap;
}

.badge-primary {
  color: var(--color-primary-700);
  background-color: var(--color-primary-50);
}

[data-theme="dark"] .badge-primary {
  color: var(--color-primary-500);
}

.badge-secondary {
  color: var(--color-secondary-700);
  background-color: var(--color-secondary-50);
}

[data-theme="dark"] .badge-secondary {
  color: var(--color-secondary-500);
}

.badge-accent {
  color: var(--color-accent-700);
  background-color: var(--color-accent-50);
}

[data-theme="dark"] .badge-accent {
  color: var(--color-accent-500);
}

.badge-success {
  color: var(--color-success-700);
  background-color: var(--color-success-50);
}

.badge-error {
  color: var(--color-error-700);
  background-color: var(--color-error-50);
}

.badge-n5 {
  color: white;
  background: linear-gradient(135deg, var(--color-primary-500), var(--color-primary-700));
  font-weight: var(--font-bold);
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-sm);
}

.badge-outline {
  color: var(--text-secondary);
  background-color: transparent;
  border: 1px solid var(--border-default);
}

/* Tag */
.tag {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-sm);
  font-weight: var(--font-medium);
  color: var(--text-secondary);
  background-color: var(--bg-tertiary);
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-default);
}

.tag:hover {
  color: var(--text-primary);
  background-color: var(--border-default);
}

.tag-interactive {
  cursor: pointer;
}

.tag-interactive.active {
  color: var(--color-primary-600);
  background-color: var(--color-primary-50);
}

/* ----------------------------------------
   12. Toast / Notification
   ---------------------------------------- */
.toast-container {
  position: fixed;
  top: var(--space-4);
  right: var(--space-4);
  z-index: var(--z-toast);
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  pointer-events: none;
}

@media (max-width: 640px) {
  .toast-container {
    left: var(--space-4);
    right: var(--space-4);
  }
}

.toast {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-3) var(--space-4);
  min-width: 300px;
  max-width: 420px;
  background-color: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-xl);
  pointer-events: auto;
  animation: toastSlideIn var(--duration-normal) var(--ease-bounce);
}

.toast.toast-exiting {
  animation: toastSlideOut var(--duration-normal) var(--ease-in) forwards;
}

.toast-icon {
  flex-shrink: 0;
  width: 24px;
  height: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--text-lg);
}

.toast-content {
  flex: 1;
}

.toast-title {
  font-size: var(--text-sm);
  font-weight: var(--font-semibold);
  color: var(--text-primary);
}

.toast-message {
  font-size: var(--text-xs);
  color: var(--text-secondary);
  margin-top: var(--space-0-5);
}

.toast-close {
  flex-shrink: 0;
  padding: var(--space-1);
  color: var(--text-tertiary);
  background: none;
  border: none;
  cursor: pointer;
  border-radius: var(--radius-sm);
  transition: all var(--duration-fast) var(--ease-default);
}

.toast-close:hover {
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
}

.toast-success {
  border-left: 4px solid var(--color-success-500);
}

.toast-success .toast-icon {
  color: var(--color-success-500);
}

.toast-error {
  border-left: 4px solid var(--color-error-500);
}

.toast-error .toast-icon {
  color: var(--color-error-500);
}

.toast-info {
  border-left: 4px solid var(--color-info-500);
}

.toast-info .toast-icon {
  color: var(--color-info-500);
}

.toast-warning {
  border-left: 4px solid var(--color-warning-500);
}

.toast-warning .toast-icon {
  color: var(--color-warning-500);
}

/* ----------------------------------------
   13. Form Elements
   ---------------------------------------- */
.input {
  width: 100%;
  padding: var(--space-2-5, 0.625rem) var(--space-3);
  font-size: var(--text-base);
  color: var(--text-primary);
  background-color: var(--bg-elevated);
  border: 2px solid var(--border-default);
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-default);
}

.input:focus {
  outline: none;
  border-color: var(--color-primary-500);
  box-shadow: 0 0 0 3px rgba(67, 97, 238, 0.15);
}

.input::placeholder {
  color: var(--text-tertiary);
}

/* ----------------------------------------
   14. Animations & Keyframes
   ---------------------------------------- */

/* Correct answer pulse */
@keyframes correctPulse {
  0%   { box-shadow: 0 0 0 0 rgba(16, 185, 129, 0.4); }
  50%  { box-shadow: 0 0 0 12px rgba(16, 185, 129, 0); }
  100% { box-shadow: 0 0 0 0 rgba(16, 185, 129, 0); }
}

/* Incorrect answer shake */
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  10%, 50%, 90% { transform: translateX(-6px); }
  30%, 70% { transform: translateX(6px); }
}

/* Toast slide in */
@keyframes toastSlideIn {
  from {
    transform: translateX(100%) scale(0.9);
    opacity: 0;
  }
  to {
    transform: translateX(0) scale(1);
    opacity: 1;
  }
}

/* Toast slide out */
@keyframes toastSlideOut {
  from {
    transform: translateX(0) scale(1);
    opacity: 1;
  }
  to {
    transform: translateX(100%) scale(0.9);
    opacity: 0;
  }
}

/* Fade in */
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

/* Fade slide down */
@keyframes fadeSlideDown {
  from {
    opacity: 0;
    transform: translateY(-12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Fade slide up */
@keyframes fadeSlideUp {
  from {
    opacity: 0;
    transform: translateY(16px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

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

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

/* Bounce */
@keyframes bounce {
  0%, 100% { transform: translateY(0); }
  50%      { transform: translateY(-6px); }
}

/* Pulse */
@keyframes pulse {
  0%, 100% { opacity: 1; }
  50%      { opacity: 0.5; }
}

/* Page transition */
@keyframes pageEnter {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Loading dots */
@keyframes loadingDots {
  0%, 80%, 100% { transform: scale(0); opacity: 0.5; }
  40%           { transform: scale(1); opacity: 1; }
}

/* Animation utility classes */
.animate-fade-in    { animation: fadeIn var(--duration-normal) var(--ease-out); }
.animate-slide-up   { animation: fadeSlideUp var(--duration-normal) var(--ease-out); }
.animate-slide-down { animation: fadeSlideDown var(--duration-normal) var(--ease-out); }
.animate-scale-in   { animation: scaleIn var(--duration-normal) var(--ease-bounce); }
.animate-page-enter { animation: pageEnter var(--duration-slow) var(--ease-out); }
.animate-bounce     { animation: bounce 1s infinite; }
.animate-pulse      { animation: pulse 2s infinite; }

/* Loading Spinner */
.spinner {
  width: 24px;
  height: 24px;
  border: 3px solid var(--bg-tertiary);
  border-top-color: var(--color-primary-500);
  border-radius: 50%;
  animation: spin 0.7s linear infinite;
}

.spinner-lg {
  width: 40px;
  height: 40px;
  border-width: 4px;
}

/* Loading Dots */
.loading-dots {
  display: inline-flex;
  gap: var(--space-1);
}

.loading-dots span {
  width: 8px;
  height: 8px;
  background-color: var(--color-primary-500);
  border-radius: 50%;
  animation: loadingDots 1.4s ease-in-out infinite both;
}

.loading-dots span:nth-child(1) { animation-delay: -0.32s; }
.loading-dots span:nth-child(2) { animation-delay: -0.16s; }
.loading-dots span:nth-child(3) { animation-delay: 0s; }

/* Skeleton Loading */
.skeleton {
  background: linear-gradient(
    90deg,
    var(--bg-tertiary) 25%,
    var(--bg-secondary) 50%,
    var(--bg-tertiary) 75%
  );
  background-size: 200% 100%;
  animation: skeleton-loading 1.5s ease-in-out infinite;
  border-radius: var(--radius-md);
}

@keyframes skeleton-loading {
  0%   { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}

/* ----------------------------------------
   15. Theme Toggle Button
   ---------------------------------------- */
.theme-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  padding: 0;
  font-size: var(--text-xl);
  color: var(--text-secondary);
  background: none;
  border: none;
  border-radius: var(--radius-full);
  cursor: pointer;
  transition: all var(--duration-fast) var(--ease-default);
}

.theme-toggle:hover {
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
}

/* ----------------------------------------
   16. Utility Classes
   ---------------------------------------- */

/* Text colors */
.text-primary   { color: var(--text-primary); }
.text-secondary { color: var(--text-secondary); }
.text-tertiary  { color: var(--text-tertiary); }

/* Text alignment */
.text-left   { text-align: left; }
.text-center { text-align: center; }
.text-right  { text-align: right; }

/* Font weight */
.font-light    { font-weight: var(--font-light); }
.font-regular  { font-weight: var(--font-regular); }
.font-medium   { font-weight: var(--font-medium); }
.font-semibold { font-weight: var(--font-semibold); }
.font-bold     { font-weight: var(--font-bold); }

/* Margin utilities */
.mt-1 { margin-top: var(--space-1); }
.mt-2 { margin-top: var(--space-2); }
.mt-3 { margin-top: var(--space-3); }
.mt-4 { margin-top: var(--space-4); }
.mt-6 { margin-top: var(--space-6); }
.mt-8 { margin-top: var(--space-8); }
.mb-1 { margin-bottom: var(--space-1); }
.mb-2 { margin-bottom: var(--space-2); }
.mb-3 { margin-bottom: var(--space-3); }
.mb-4 { margin-bottom: var(--space-4); }
.mb-6 { margin-bottom: var(--space-6); }
.mb-8 { margin-bottom: var(--space-8); }

/* Padding utilities */
.p-2 { padding: var(--space-2); }
.p-3 { padding: var(--space-3); }
.p-4 { padding: var(--space-4); }
.p-6 { padding: var(--space-6); }
.p-8 { padding: var(--space-8); }

/* Display */
.hidden { display: none; }
.block  { display: block; }

/* Overflow */
.overflow-hidden { overflow: hidden; }

/* Screen reader only */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* ----------------------------------------
   17. Responsive Breakpoints
   ---------------------------------------- */
/* Mobile: < 640px   (default, no media query needed) */
/* Tablet: >= 768px  */
/* Desktop: >= 1024px */
/* Wide: >= 1280px   */

@media (max-width: 639px) {
  h1, .h1 { font-size: var(--text-3xl); }
  h2, .h2 { font-size: var(--text-2xl); }
  h3, .h3 { font-size: var(--text-xl); }

  .flashcard-container {
    height: 240px;
  }

  .flashcard-front .kanji {
    font-size: var(--text-4xl);
  }
}

/* ----------------------------------------
   18. Print Styles
   ---------------------------------------- */
@media print {
  body {
    background: white;
    color: black;
  }

  .navbar,
  .toast-container,
  .theme-toggle {
    display: none !important;
  }

  .card {
    break-inside: avoid;
    border: 1px solid #ccc;
    box-shadow: none;
  }
}

/* ----------------------------------------
   19. Reduced Motion Preferences
   ---------------------------------------- */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  .flashcard {
    transition: none;
  }

  .progress-bar::after {
    animation: none;
  }
}

/* ----------------------------------------
   20. Divider & Decorative Elements
   ---------------------------------------- */
.divider {
  width: 100%;
  height: 1px;
  background-color: var(--border-default);
  margin: var(--space-6) 0;
}

.divider-decorated {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  color: var(--text-tertiary);
  font-size: var(--text-sm);
}

.divider-decorated::before,
.divider-decorated::after {
  content: '';
  flex: 1;
  height: 1px;
  background-color: var(--border-default);
}

/* Japanese Wave Decoration */
.wave-decoration {
  position: relative;
  overflow: hidden;
}

.wave-decoration::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 6px;
  background: repeating-linear-gradient(
    90deg,
    var(--color-primary-200) 0px,
    var(--color-primary-200) 2px,
    transparent 2px,
    transparent 8px
  );
  opacity: 0.5;
}

/* ----------------------------------------
   21. Stat / Score Card
   ---------------------------------------- */
.stat-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: var(--space-5);
  background-color: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-xl);
  text-align: center;
}

.stat-value {
  font-size: var(--text-3xl);
  font-weight: var(--font-bold);
  color: var(--color-primary-500);
  line-height: 1;
}

.stat-label {
  font-size: var(--text-sm);
  color: var(--text-secondary);
  margin-top: var(--space-2);
}

/* ----------------------------------------
   22. Timer Component
   ---------------------------------------- */
.timer {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-3);
  font-size: var(--text-lg);
  font-weight: var(--font-semibold);
  font-variant-numeric: tabular-nums;
  color: var(--text-primary);
  background-color: var(--bg-tertiary);
  border-radius: var(--radius-md);
}

.timer.warning {
  color: var(--color-warning-600);
  background-color: var(--color-warning-50);
}

.timer.danger {
  color: var(--color-error-600);
  background-color: var(--color-error-50);
  animation: pulse 1s infinite;
}