:root {
  color-scheme: dark;
  --bg-base: #000000;
  --bg-surface: #0f0f0f;
  --bg-elevated: #1a1a1a;
  --bg-input: #111111;
  
  --border-subtle: rgba(255, 255, 255, 0.05);
  --border-default: rgba(255, 255, 255, 0.1);
  --border-strong: rgba(255, 255, 255, 0.2);
  
  --text-primary: #ffffff;
  --text-secondary: rgba(255, 255, 255, 0.7);
  --text-muted: rgba(255, 255, 255, 0.45);
  
  --accent: #e8001d;
  --accent-dim: rgba(232, 0, 29, 0.1);
  
  --tag-bg: #1e1e1e;
  --tag-text: #999999;

  /* ui-ux-pro-max tokens */
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-full: 999px;

  --space-section: 112px;
  --space-group: 64px;
  --space-element: 24px;

  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-7: 48px;
  --space-8: 64px;

  --font-size-base: 16px;
  --font-size-ui: 12px;
  --font-size-title: 48px;
  --font-size-section: 24px;

  font-family: "Inter", system-ui, -apple-system, sans-serif;
  background: var(--bg-base);
  color: var(--text-primary);
  line-height: 1.6;
}

[data-theme="light"] {
  color-scheme: light;
  --bg-base: #f7f7f7;
  --bg-surface: #ffffff;
  --bg-elevated: #efefef;
  --bg-input: #ffffff;
  
  --border-subtle: rgba(0, 0, 0, 0.04);
  --border-default: rgba(0, 0, 0, 0.08);
  --border-strong: rgba(0, 0, 0, 0.15);
  
  --text-primary: #000000;
  --text-secondary: rgba(0, 0, 0, 0.6);
  --text-muted: rgba(0, 0, 0, 0.4);
  
  --accent: #e8001d;
  --accent-dim: rgba(232, 0, 29, 0.05);
}

[data-font-size="small"] {
  --font-size-base: 14px;
  --font-size-ui: 11px;
  --font-size-title: 36px;
  --font-size-section: 20px;
}

[data-font-size="large"] {
  --font-size-base: 18px;
  --font-size-ui: 14px;
  --font-size-title: 64px;
  --font-size-section: 32px;
}

[data-font-size="extra-large"] {
  --font-size-base: 20px;
  --font-size-ui: 16px;
  --font-size-title: 80px;
  --font-size-section: 40px;
}

* {
  box-sizing: border-box;
  -webkit-font-smoothing: antialiased;
}

html, body, #root {
  min-height: 100%;
}

body {
  margin: 0;
  background: var(--bg-base);
  color: var(--text-primary);
  font-size: var(--font-size-base);
}

/* Typography Tokens */
.text-hero {
  font-family: "Barlow Condensed", "Oswald", sans-serif;
  font-size: var(--font-size-title);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  line-height: 1.1;
}

.text-section {
  font-family: "Barlow Condensed", "Oswald", sans-serif;
  font-size: var(--font-size-section);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.text-headline {
  font-size: 1.25rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.text-subhead {
  font-size: 1.125rem;
  color: var(--text-secondary);
}

a {
  color: inherit;
  text-decoration: none;
  transition: opacity 0.2s ease;
}

a:hover {
  opacity: 0.8;
}

button, input, textarea {
  font: inherit;
}

button, input, textarea, .tree-link, .entry-question-button {
  transition: all 0.2s ease;
}

input, textarea {
  width: 100%;
  padding: 12px 16px;
  border: 1px solid var(--border-default);
  border-radius: var(--radius-md);
  background: var(--bg-input);
  color: var(--text-primary);
  font-size: var(--font-size-base);
}

input:focus, textarea:focus {
  outline: none;
  border-color: var(--text-muted);
  background: var(--bg-elevated);
}

.button-primary {
  background: #ffffff;
  color: #000000;
  padding: 12px 24px;
  font-weight: 600;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-size: var(--font-size-ui);
}

.button-primary:hover {
  background: rgba(255, 255, 255, 0.9);
  transform: translateY(-1px);
}

.button-primary:disabled {
  background: var(--bg-elevated);
  color: var(--text-muted);
  cursor: not-allowed;
  transform: none;
}

.button-ghost {
  background: transparent;
  color: var(--text-primary);
  border: 1px solid var(--border-default);
  padding: 12px 24px;
  border-radius: var(--radius-md);
  cursor: pointer;
}

.button-ghost:hover {
  background: var(--bg-surface);
  border-color: var(--border-strong);
}

.icon-button {
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: transparent;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-full);
  color: var(--text-secondary);
  cursor: pointer;
  flex-shrink: 0;
}

.icon-button:hover {
  background: var(--bg-elevated);
  color: var(--text-primary);
  border-color: var(--border-default);
}

.top-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 72px;
  background: rgba(0, 0, 0, 0.8);
  backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 32px;
  z-index: 100;
}

.top-nav-left, .top-nav-right {
  display: flex;
  align-items: center;
  flex: 1;
}

.top-nav-center {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: center;
}

.top-nav-right {
  justify-content: flex-end;
}

.sidebar {
  position: fixed;
  top: 72px;
  left: 0;
  bottom: 0;
  width: 260px;
  background: var(--bg-base);
  border-right: 1px solid var(--border-subtle);
  z-index: 90;
  transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: var(--border-strong) transparent;
}

.sidebar-closed .sidebar {
  transform: translateX(-100%);
}

.sidebar-open .sidebar {
  transform: translateX(0);
}

.app-main {
  padding-top: 72px;
  transition: padding-left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.sidebar-open .app-main {
  padding-left: 260px;
}

.sidebar-closed .app-main {
  padding-left: 0;
}

.sidebar-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  z-index: 85;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s ease;
}

.sidebar-backdrop.open {
  opacity: 1;
  pointer-events: auto;
}

@media (max-width: 960px) {
  .sidebar-open .app-main {
    padding-left: 0;
  }
  
  .sidebar {
    z-index: 1000;
    top: 0;
    height: 100%;
  }

  .top-nav {
    padding: 0 16px;
    height: 64px;
  }

  .app-main {
    padding-top: 64px;
  }
}

@media (max-width: 720px) {
  :root {
    --space-section: 64px;
    --space-group: 32px;
    --space-element: 16px;
    --font-size-title: 36px;
    --font-size-section: 20px;
  }

  .content-wrap {
    padding: var(--space-group) 16px var(--space-section);
  }

  .card-header-row {
    flex-direction: column;
    align-items: stretch !important;
    gap: 24px;
  }

  .card-header-actions {
    margin-left: 0 !important;
    display: grid !important;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
  }

  .text-hero {
    font-size: var(--font-size-title) !important;
  }

  .card-grid {
    grid-template-columns: 1fr;
  }

  .button-primary, .button-ghost {
    min-height: 44px;
    display: flex;
    align-items: center;
    justify-content: center;
  }

  .mobile-modal-full {
    position: fixed !important;
    inset: 0 !important;
    width: 100% !important;
    height: 100% !important;
    max-width: none !important;
    max-height: none !important;
    border-radius: 0 !important;
    padding: 0 !important;
  }
}

.content-wrap {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-group) 32px var(--space-section);
}

.section-block {
  margin-bottom: var(--space-section);
}

.section-title {
  composes: text-section;
  margin-bottom: var(--space-element);
}

/* Premium Card Design */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--space-element);
}

.subject-card {
  background: var(--bg-surface);
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid var(--border-subtle);
  transition: all 0.3s ease;
  height: 100%;
  display: flex;
  flex-direction: column;
}

.subject-card:hover {
  border-color: var(--border-strong);
  transform: translateY(-4px);
  background: var(--bg-elevated);
}

.subject-card-header {
  padding: 24px;
  border-bottom: 1px solid var(--border-subtle);
}

.subject-card-header span {
  font-family: "Barlow Condensed", sans-serif;
  font-size: 1.5rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.02em;
}

.subject-card-body {
  padding: 24px;
  color: var(--text-secondary);
  font-size: 0.875rem;
  flex-grow: 1;
}

/* Entry Row Styling */
.entry-row {
  border-bottom: 1px solid var(--border-subtle);
  padding: 24px 0;
}

.entry-question-row {
  display: flex;
  align-items: center;
  gap: 16px;
}

.entry-question-button {
  flex: 1;
  font-size: calc(var(--font-size-base) * 1.125);
  font-weight: 500;
  color: var(--text-primary);
  text-align: left;
}

.entry-answer {
  margin-top: 24px;
  color: var(--text-secondary);
  line-height: 1.8;
  display: none;
  font-size: var(--font-size-base);
}

.entry-answer.expanded {
  display: block;
}

/* Search Box */
.search-box input {
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  height: 44px;
  border-radius: var(--radius-full);
  padding: 0 20px;
}

.search-box input:focus {
  border-color: var(--border-strong);
  width: 100%;
}

/* Sidebar & Tree */
.tree-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.tree-link {
  display: block;
  padding: 10px 24px;
  font-size: var(--font-size-ui);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-secondary);
  border-left: 2px solid transparent;
  transition: all 0.2s ease;
}

.tree-link:hover {
  background: var(--bg-surface);
  color: var(--text-primary);
}

.tree-link.active {
  color: var(--accent);
  border-left-color: var(--accent);
  background: var(--accent-dim);
}

.tree-link.drop-target {
  background: var(--accent-dim);
  border-left-color: var(--accent);
}

.sidebar-header {
  padding: 24px;
  font-family: "Barlow Condensed", sans-serif;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-muted);
  font-size: 0.75rem;
}

/* Modals & Overlays */
.settings-dropdown {
  position: absolute;
  top: calc(100% + 12px);
  right: 0;
  width: 280px;
  background: var(--bg-surface);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-lg);
  box-shadow: 0 24px 48px rgba(0, 0, 0, 0.4);
  padding: 24px;
  z-index: 150;
}

.settings-section {
  margin-bottom: 24px;
}

.settings-label {
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.settings-row {
  display: flex;
  gap: 8px;
}

.settings-row button {
  flex: 1;
  padding: 8px;
  font-size: 0.75rem;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-default);
  background: var(--bg-input);
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  cursor: pointer;
  transition: all 0.2s ease;
}

.settings-row button.active {
  background: var(--accent);
  color: #ffffff;
  border-color: var(--accent);
  box-shadow: 0 4px 12px var(--accent-dim);
}

.mode-toggle {
  display: flex;
  background: var(--bg-input);
  padding: 4px;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-subtle);
}

.mode-toggle button {
  border: 0;
  background: transparent;
  color: var(--text-muted);
  padding: 8px 16px;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  font-size: 11px;
  font-weight: 600;
  cursor: pointer;
  border-radius: calc(var(--radius-md) - 2px);
  transition: all 0.2s ease;
}

.mode-toggle button.active {
  background: var(--accent);
  color: #ffffff;
  box-shadow: 0 4px 12px var(--accent-dim);
}

.is-hidden {
  display: none !important;
}

/* Modals & Overlays */
.settings-menu-container {
  position: relative;
}

.settings-dropdown {
  position: absolute;
  top: calc(100% + 12px);
  right: 0;
  width: 280px;
  background: var(--bg-surface);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-lg);
  box-shadow: 0 32px 64px rgba(0, 0, 0, 0.6);
  padding: 24px;
  z-index: 1000;
  pointer-events: auto;
}