:root {
  --color-primary: #3B82F6;
  --color-primary-hover: #2563EB;
  --color-primary-light: #DBEAFE;
  --color-secondary: #6B7280;
  --color-success: #22C55E;
  --color-warning: #F59E0B;
  --color-error: #EF4444;
  --color-bg-primary: #FFFFFF;
  --color-bg-secondary: #F9FAFB;
  --color-bg-tertiary: #F3F4F6;
  --color-bg-hover: #E5E7EB;
  --color-text-primary: #111827;
  --color-text-secondary: #4B5563;
  --color-text-muted: #9CA3AF;
  --color-text-inverse: #FFFFFF;
  --color-border: #E5E7EB;
  --color-border-focus: #3B82F6;
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 32px;
  --space-2xl: 48px;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --radius-full: 9999px;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0/0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0/0.1), 0 2px 4px -2px rgb(0 0 0/0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0/0.1), 0 4px 6px -4px rgb(0 0 0/0.1);
  --shadow-xl: 0 20px 25px -5px rgb(0 0 0/0.1), 0 8px 10px -6px rgb(0 0 0/0.1);
  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
  --z-dropdown: 100;
  --z-sticky: 200;
  --z-modal: 300;
  --z-toast: 400;
  --sidebar-width: 280px;
  --header-height: 64px;
  --max-content-width: 900px;
}

[data-theme="dark"] {
  --color-primary: #60A5FA;
  --color-primary-hover: #93C5FD;
  --color-primary-light: #1E3A5F;
  --color-secondary: #9CA3AF;
  --color-bg-primary: #111827;
  --color-bg-secondary: #1F2937;
  --color-bg-tertiary: #374151;
  --color-bg-hover: #4B5563;
  --color-text-primary: #F9FAFB;
  --color-text-secondary: #D1D5DB;
  --color-text-muted: #9CA3AF;
  --color-text-inverse: #111827;
  --color-border: #374151;
  --color-border-focus: #60A5FA;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0/0.3);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0/0.4), 0 2px 4px -2px rgb(0 0 0/0.3);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0/0.4), 0 4px 6px -4px rgb(0 0 0/0.3);
  --shadow-xl: 0 20px 25px -5px rgb(0 0 0/0.4), 0 8px 10px -6px rgb(0 0 0/0.3);
}

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

body {
  font-family: var(--font-sans);
  font-size: var(--font-size-base);
  color: var(--color-text-primary);
  background: var(--color-bg-primary);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

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

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: 10px 20px;
  font-size: var(--font-size-sm);
  font-weight: 500;
  border-radius: var(--radius-md);
  border: none;
  cursor: pointer;
  transition: all var(--transition-fast);
}

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

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

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

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

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

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

.btn-lg {
  padding: 14px 28px;
  font-size: var(--font-size-base);
}

.btn-icon {
  padding: 8px;
}

.w-full {
  width: 100%;
}

.flex {
  display: flex;
}

.items-center {
  align-items: center;
}

.gap-md {
  gap: var(--space-md);
}

/* Landing Page */
.landing {
  min-height: 100vh;
}

.landing-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--space-md) var(--space-xl);
  max-width: 1200px;
  margin: 0 auto;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: var(--font-size-lg);
  font-weight: 700;
  color: var(--color-text-primary);
}

.nav-logo svg {
  width: 24px;
  height: 24px;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
}

.nav-link {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

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

.hero {
  text-align: center;
  padding: var(--space-2xl) var(--space-xl);
  max-width: 800px;
  margin: 0 auto;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 6px 16px;
  background: var(--color-primary-light);
  color: var(--color-primary);
  border-radius: var(--radius-full);
  font-size: var(--font-size-sm);
  font-weight: 500;
  margin-bottom: var(--space-lg);
}

.hero-title {
  font-size: var(--font-size-3xl);
  font-weight: 800;
  line-height: 1.1;
  margin-bottom: var(--space-md);
}

.hero-title span {
  color: var(--color-primary);
}

.hero-subtitle {
  font-size: var(--font-size-lg);
  color: var(--color-text-secondary);
  max-width: 600px;
  margin: 0 auto var(--space-xl);
}

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

.features {
  padding: var(--space-2xl) var(--space-xl);
  max-width: 1200px;
  margin: 0 auto;
}

.features-header {
  text-align: center;
  margin-bottom: var(--space-xl);
}

.features-title {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  margin-bottom: var(--space-sm);
}

.features-subtitle {
  color: var(--color-text-secondary);
}

.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--space-lg);
}

.feature-card {
  padding: var(--space-lg);
  background: var(--color-bg-secondary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
}

.feature-icon {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  margin-bottom: var(--space-md);
}

.feature-title {
  font-size: var(--font-size-lg);
  font-weight: 600;
  margin-bottom: var(--space-sm);
}

.feature-desc {
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

/* Login Page */
.login-page {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-xl);
  background: var(--color-bg-secondary);
}

.login-card {
  width: 100%;
  max-width: 400px;
  padding: var(--space-xl);
  background: var(--color-bg-primary);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-lg);
  text-align: center;
}

.login-logo {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  font-size: var(--font-size-xl);
  font-weight: 700;
  margin-bottom: var(--space-lg);
}

.login-logo svg {
  width: 28px;
  height: 28px;
}

.login-title {
  font-size: var(--font-size-xl);
  font-weight: 600;
  margin-bottom: var(--space-sm);
}

.login-subtitle {
  color: var(--color-text-secondary);
  margin-bottom: var(--space-xl);
}

.google-btn {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  padding: 12px;
  background: var(--color-bg-primary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: var(--font-size-base);
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.google-btn:hover {
  background: var(--color-bg-secondary);
}

.google-btn svg {
  width: 20px;
  height: 20px;
}

.login-terms {
  margin-top: var(--space-lg);
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
}

/* App Layout */
.app-layout {
  display: flex;
  min-height: 100vh;
}

.sidebar {
  width: var(--sidebar-width);
  background: var(--color-bg-secondary);
  border-right: 1px solid var(--color-border);
  display: flex;
  flex-direction: column;
  position: fixed;
  top: 0;
  left: 0;
  bottom: 0;
  z-index: var(--z-sticky);
}

.sidebar-header {
  padding: var(--space-md);
  border-bottom: 1px solid var(--color-border);
}

.sidebar-content {
  flex: 1;
  overflow-y: auto;
  padding: var(--space-md);
}

.sidebar-footer {
  padding: var(--space-md);
  border-top: 1px solid var(--color-border);
}

.sidebar-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  z-index: calc(var(--z-sticky) - 1);
}

.main-content {
  flex: 1;
  margin-left: var(--sidebar-width);
  display: flex;
  flex-direction: column;
}

.page-header {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md) var(--space-lg);
  border-bottom: 1px solid var(--color-border);
  background: var(--color-bg-primary);
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
}

.page-content {
  flex: 1;
  padding: var(--space-lg);
  overflow-y: auto;
}

.container {
  max-width: var(--max-content-width);
  margin: 0 auto;
}

/* Chat List */
.chat-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
}

.chat-item {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background var(--transition-fast);
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

.chat-item:hover {
  background: var(--color-bg-hover);
  color: var(--color-text-primary);
}

.chat-item.active {
  background: var(--color-primary-light);
  color: var(--color-primary);
}

/* Dashboard Search */
.dashboard-search {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: 10px 16px;
  background: var(--color-bg-tertiary);
  border-radius: var(--radius-md);
  flex: 1;
  max-width: 400px;
}

.dashboard-search svg {
  width: 18px;
  height: 18px;
  color: var(--color-text-muted);
}

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

/* Chat Container */
.chat-container {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

.chat-header {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  border-bottom: 1px solid var(--color-border);
  background: var(--color-bg-primary);
}

.chat-subject {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
}

.chat-title {
  flex: 1;
  font-size: var(--font-size-base);
  font-weight: 600;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.chat-messages {
  flex: 1;
  overflow-y: auto;
  padding: var(--space-lg);
}

.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: var(--space-2xl);
}

.empty-state-icon {
  font-size: 48px;
  margin-bottom: var(--space-md);
}

.empty-state-title {
  font-size: var(--font-size-xl);
  font-weight: 600;
  margin-bottom: var(--space-sm);
}

.empty-state-desc {
  color: var(--color-text-secondary);
}

.message {
  display: flex;
  gap: var(--space-md);
  margin-bottom: var(--space-lg);
}

.message-avatar {
  width: 32px;
  height: 32px;
  border-radius: var(--radius-full);
  background: var(--color-bg-tertiary);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: var(--font-size-sm);
  flex-shrink: 0;
}

.message.user .message-avatar {
  background: var(--color-primary);
  color: var(--color-text-inverse);
}

.message.assistant .message-avatar {
  background: var(--color-bg-tertiary);
}

.message-content {
  flex: 1;
  line-height: 1.6;
}

.message-actions {
  display: flex;
  gap: var(--space-xs);
  margin-top: var(--space-sm);
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.message:hover .message-actions {
  opacity: 1;
}

/* Chat Input */
.chat-input-area {
  padding: var(--space-md);
  border-top: 1px solid var(--color-border);
  background: var(--color-bg-primary);
}

.chat-input-wrapper {
  display: flex;
  align-items: flex-end;
  gap: var(--space-sm);
  padding: var(--space-sm);
  background: var(--color-bg-tertiary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
}

.chat-input-wrapper:focus-within {
  border-color: var(--color-border-focus);
}

.chat-input {
  flex: 1;
  border: none;
  background: transparent;
  padding: var(--space-sm);
  font-size: var(--font-size-base);
  font-family: var(--font-sans);
  resize: none;
  outline: none;
  max-height: 150px;
}

.send-btn {
  width: 36px;
  height: 36px;
  border-radius: var(--radius-md);
  background: var(--color-primary);
  color: var(--color-text-inverse);
  border: none;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.send-btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.send-btn svg {
  width: 18px;
  height: 18px;
}

/* Settings */
.settings-section {
  padding: var(--space-lg);
  background: var(--color-bg-secondary);
  border-radius: var(--radius-lg);
  margin-bottom: var(--space-md);
}

.profile-section {
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

.profile-avatar {
  width: 80px;
  height: 80px;
  border-radius: var(--radius-full);
  background: var(--color-bg-tertiary);
}

.profile-info h3 {
  font-size: var(--font-size-lg);
  font-weight: 600;
}

/* Mobile Responsive */
@media (max-width: 768px) {
  .sidebar {
    transform: translateX(-100%);
    transition: transform var(--transition-normal);
  }

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

  .sidebar-overlay.open {
    display: block;
  }

  .main-content {
    margin-left: 0;
  }

  #menu-btn {
    display: flex !important;
  }

  .nav-links {
    display: none;
  }

  .hero-title {
    font-size: var(--font-size-2xl);
  }

  .hero-cta {
    flex-direction: column;
  }
}

/* Theme Toggle */
.theme-toggle {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-md);
  background: var(--color-bg-tertiary);
  border-radius: var(--radius-md);
}

.theme-toggle button {
  padding: var(--space-xs) var(--space-sm);
  border: none;
  background: transparent;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

.theme-toggle button.active {
  background: var(--color-bg-primary);
  color: var(--color-text-primary);
  box-shadow: var(--shadow-sm);
}

/* Subject Cards */
.subjects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: var(--space-md);
}

.subject-card {
  padding: var(--space-lg);
  background: var(--color-bg-secondary);
  border-radius: var(--radius-lg);
  border: 1px solid var(--color-border);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.subject-card:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-md);
}

.subject-card-title {
  font-weight: 600;
  margin-bottom: var(--space-sm);
}

.subject-card-desc {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

/* Loading Spinner */
.spinner {
  width: 20px;
  height: 20px;
  border: 2px solid var(--color-bg-tertiary);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

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

/* Toast Notifications */
.toast {
  position: fixed;
  bottom: var(--space-lg);
  right: var(--space-lg);
  padding: var(--space-md) var(--space-lg);
  background: var(--color-bg-primary);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--color-border);
  z-index: var(--z-toast);
  animation: slideIn 0.3s ease;
}

@keyframes slideIn {
  from {
    transform: translateY(100%);
    opacity: 0;
  }
  to {
    transform: translateY(0);
    opacity: 1;
  }
}

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

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