/* ============================================================================
   DESIGN PHILOSOPHY
   ============================================================================
   - Simple, clean design that doesn't distract from functionality
   - Accessible by default (focus states, contrast, semantic HTML)
   - Responsive without media queries (using flexible units)
   - CSS custom properties for easy theming
   ============================================================================ */

:root {
  /* Color palette - simple and accessible */
  --color-primary: #0066cc;
  --color-primary-hover: #0052a3;
  --color-text: #1a1a1a;
  --color-text-secondary: #666;
  --color-border: #e0e0e0;
  --color-background: #ffffff;
  --color-background-secondary: #f5f5f5;
  --color-success: #22c55e;
  --color-danger: #ef4444;

  /* Spacing scale */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;

  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
    'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
    sans-serif;
  --font-size-base: 16px;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.5rem;
  --font-size-sm: 0.875rem;

  /* Effects */
  --border-radius: 8px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
  --transition-speed: 150ms;
}

/* ============================================================================
   BASE STYLES
   ============================================================================ */

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

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  color: var(--color-text);
  background-color: var(--color-background-secondary);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ============================================================================
   APP LAYOUT
   ============================================================================ */

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

.app-header {
  background-color: var(--color-background);
  border-bottom: 1px solid var(--color-border);
  padding: var(--space-xl) var(--space-lg);
  text-align: center;
}

.app-header h1 {
  font-size: var(--font-size-xl);
  margin-bottom: var(--space-xs);
}

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

.app-main {
  flex: 1;
  max-width: 600px;
  width: 100%;
  margin: 0 auto;
  padding: var(--space-xl) var(--space-lg);
}

.app-footer {
  background-color: var(--color-background);
  border-top: 1px solid var(--color-border);
  padding: var(--space-lg);
  text-align: center;
  color: var(--color-text-secondary);
  font-size: var(--font-size-sm);
}

/* ============================================================================
   TASK INPUT FORM
   ============================================================================ */

.task-input-form {
  display: flex;
  gap: var(--space-sm);
  margin-bottom: var(--space-lg);
}

.task-input {
  flex: 1;
  padding: var(--space-md);
  border: 2px solid var(--color-border);
  border-radius: var(--border-radius);
  font-size: var(--font-size-base);
  font-family: inherit;
  transition: border-color var(--transition-speed);
}

.task-input:focus {
  outline: none;
  border-color: var(--color-primary);
}

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

.add-button {
  padding: var(--space-md) var(--space-lg);
  background-color: var(--color-primary);
  color: white;
  border: none;
  border-radius: var(--border-radius);
  font-size: var(--font-size-base);
  font-weight: 600;
  cursor: pointer;
  transition: background-color var(--transition-speed);
  white-space: nowrap;
}

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

.add-button:active {
  transform: translateY(1px);
}

/* ============================================================================
   TASK STATS
   ============================================================================ */

.task-stats {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-md);
  background-color: var(--color-background);
  border-radius: var(--border-radius);
  margin-bottom: var(--space-lg);
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  box-shadow: var(--shadow-sm);
}

.divider {
  opacity: 0.5;
}

/* ============================================================================
   TASK LIST
   ============================================================================ */

.task-list {
  list-style: none;
  background-color: var(--color-background);
  border-radius: var(--border-radius);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
}

.task-item {
  display: flex;
  align-items: center;
  padding: var(--space-md);
  border-bottom: 1px solid var(--color-border);
  transition: background-color var(--transition-speed);
}

.task-item:last-child {
  border-bottom: none;
}

.task-item:hover {
  background-color: var(--color-background-secondary);
}

.task-label {
  flex: 1;
  display: flex;
  align-items: center;
  gap: var(--space-md);
  cursor: pointer;
  user-select: none;
}

.task-label input[type="checkbox"] {
  width: 20px;
  height: 20px;
  cursor: pointer;
  flex-shrink: 0;
}

.task-text {
  flex: 1;
  word-break: break-word;
}

.task-item.completed .task-text {
  color: var(--color-text-secondary);
  text-decoration: line-through;
}

.delete-button {
  width: 32px;
  height: 32px;
  border: none;
  background-color: transparent;
  color: var(--color-text-secondary);
  font-size: 24px;
  line-height: 1;
  cursor: pointer;
  border-radius: 4px;
  transition: all var(--transition-speed);
  flex-shrink: 0;
}

.delete-button:hover {
  background-color: var(--color-danger);
  color: white;
}

/* ============================================================================
   EMPTY STATE
   ============================================================================ */

.empty-state {
  padding: var(--space-xl);
  text-align: center;
  color: var(--color-text-secondary);
  background-color: var(--color-background);
  border-radius: var(--border-radius);
  box-shadow: var(--shadow-sm);
}

/* ============================================================================
   ACTIONS
   ============================================================================ */

.actions {
  margin-top: var(--space-lg);
  display: flex;
  justify-content: center;
}

.clear-completed {
  padding: var(--space-sm) var(--space-lg);
  background-color: transparent;
  color: var(--color-text-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius);
  font-size: var(--font-size-sm);
  cursor: pointer;
  transition: all var(--transition-speed);
}

.clear-completed:hover {
  background-color: var(--color-background);
  border-color: var(--color-danger);
  color: var(--color-danger);
}

/* ============================================================================
   ACCESSIBILITY
   ============================================================================ */

/* Focus states for keyboard navigation */
button:focus-visible,
input:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* Reduce motion for users who prefer it */
@media (prefers-reduced-motion: reduce) {
  * {
    transition: none !important;
    animation: none !important;
  }
}

/* Dark mode support - respects user preference */
@media (prefers-color-scheme: dark) {
  :root {
    --color-primary: #3b82f6;
    --color-primary-hover: #2563eb;
    --color-text: #f5f5f5;
    --color-text-secondary: #a3a3a3;
    --color-border: #404040;
    --color-background: #1a1a1a;
    --color-background-secondary: #0a0a0a;
  }
}