/* ================================
   CSS Variables & Design Tokens
   ================================ */
:root {
  /* Colors - Light Mode */
  --color-primary: #6366f1;
  --color-primary-hover: #4f46e5;
  --color-primary-light: rgba(99, 102, 241, 0.1);
  
  --color-success: #10b981;
  --color-danger: #ef4444;
  --color-warning: #f59e0b;
  
  --color-bg: #f8fafc;
  --color-bg-secondary: #ffffff;
  --color-bg-tertiary: #f1f5f9;
  
  --color-text: #0f172a;
  --color-text-secondary: #64748b;
  --color-text-muted: #94a3b8;
  
  --color-border: #e2e8f0;
  --color-border-hover: #cbd5e1;
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -2px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.1);
  
  /* Glass effect */
  --glass-bg: rgba(255, 255, 255, 0.7);
  --glass-border: rgba(255, 255, 255, 0.3);
  
  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  
  /* Border Radius */
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-2xl: 1.5rem;
  --radius-full: 9999px;
  
  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
  --transition-slow: 350ms ease;
  
  /* Typography */
  --font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 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: 1.875rem;
}

/* Dark Mode */
[data-theme="dark"] {
  --color-primary: #818cf8;
  --color-primary-hover: #a5b4fc;
  --color-primary-light: rgba(129, 140, 248, 0.15);
  
  --color-bg: #0f172a;
  --color-bg-secondary: #1e293b;
  --color-bg-tertiary: #334155;
  
  --color-text: #f1f5f9;
  --color-text-secondary: #94a3b8;
  --color-text-muted: #64748b;
  
  --color-border: #334155;
  --color-border-hover: #475569;
  
  --glass-bg: rgba(30, 41, 59, 0.8);
  --glass-border: rgba(51, 65, 85, 0.5);
  
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: 1.6;
  color: var(--color-text);
  background: var(--color-bg);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

#app {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ================================
   Header
   ================================ */
.header {
  background: var(--glass-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
  position: sticky;
  top: 0;
  z-index: 100;
}

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

.logo {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  text-decoration: none;
  color: var(--color-text);
}

.logo-icon {
  width: 32px;
  height: 32px;
  color: var(--color-primary);
}

.logo-text {
  font-size: var(--font-size-xl);
  font-weight: 700;
  background: linear-gradient(135deg, var(--color-primary), #a855f7);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
}

/* ================================
   Buttons
   ================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-sm) var(--spacing-lg);
  font-family: inherit;
  font-size: var(--font-size-sm);
  font-weight: 500;
  line-height: 1.5;
  border: none;
  border-radius: var(--radius-lg);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
}

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

.btn-primary {
  background: linear-gradient(135deg, var(--color-primary), #8b5cf6);
  color: white;
  box-shadow: 0 4px 14px 0 rgba(99, 102, 241, 0.4);
}

.btn-primary:hover:not(:disabled) {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px 0 rgba(99, 102, 241, 0.5);
}

.btn-primary:active:not(:disabled) {
  transform: translateY(0);
}

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

.btn-secondary:hover:not(:disabled) {
  background: var(--color-border);
  border-color: var(--color-border-hover);
}

.btn-sm {
  padding: var(--spacing-xs) var(--spacing-md);
  font-size: var(--font-size-xs);
}

.btn-lg {
  padding: var(--spacing-md) var(--spacing-xl);
  font-size: var(--font-size-base);
}

.btn-icon {
  width: 18px;
  height: 18px;
  flex-shrink: 0;
}

.icon-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: none;
  border-radius: var(--radius-lg);
  background: var(--color-bg-tertiary);
  color: var(--color-text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.icon-btn:hover {
  background: var(--color-border);
  color: var(--color-text);
}

.icon-btn.danger:hover {
  background: rgba(239, 68, 68, 0.1);
  color: var(--color-danger);
}

.icon-btn .icon {
  width: 20px;
  height: 20px;
}

/* Theme Toggle */
#themeToggle .moon-icon { display: none; }
[data-theme="dark"] #themeToggle .sun-icon { display: none; }
[data-theme="dark"] #themeToggle .moon-icon { display: block; }

/* Language Selector */
.lang-select {
  padding: var(--spacing-xs) var(--spacing-sm);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg-secondary);
  color: var(--color-text);
  font-size: var(--font-size-sm);
  cursor: pointer;
}

/* ================================
   Main Content
   ================================ */
.main {
  flex: 1;
  padding: var(--spacing-xl) var(--spacing-lg);
}

.container {
  max-width: 900px;
  margin: 0 auto;
}

/* ================================
   Footer
   ================================ */
.footer {
  text-align: center;
  padding: var(--spacing-lg);
  color: var(--color-text-muted);
  font-size: var(--font-size-sm);
}

/* ================================
   Utilities
   ================================ */
.hidden {
  display: none !important;
}

/* ================================
   Responsive
   ================================ */
@media (max-width: 640px) {
  .header-content {
    padding: var(--spacing-sm) var(--spacing-md);
  }
  
  .logo-text {
    font-size: var(--font-size-lg);
  }
  
  .main {
    padding: var(--spacing-md);
  }
}