/* ============================================
   CSS Variables for Theming
   ============================================ */
:root {
  /* Light Theme Colors */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --text-primary: #1e293b;
  --text-secondary: #64748b;
  --text-muted: #94a3b8;
  --border-color: #e2e8f0;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);

  /* Accent Colors */
  --primary: #6366f1;
  --primary-hover: #4f46e5;
  --secondary: #8b5cf6;
  --success: #10b981;
  --warning: #f59e0b;
  --danger: #ef4444;
  --info: #3b82f6;

  /* Priority Colors */
  --priority-high: #ef4444;
  --priority-medium: #f59e0b;
  --priority-low: #10b981;

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

  /* Border Radius */
  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;

  /* Transitions */
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 350ms ease;

  /* Layout */
  --sidebar-width: 280px;
  --header-height: 64px;
}

/* Dark Theme */
[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --text-primary: #f1f5f9;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --border-color: #334155;
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.6);
}

/* ============================================
   Reset & Base Styles
   ============================================ */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif;
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  line-height: 1.6;
  transition: background-color var(--transition-base),
    color var(--transition-base);
}

/* ============================================
   Header
   ============================================ */
.header {
  background-color: var(--bg-primary);
  border-bottom: 1px solid var(--border-color);
  height: var(--header-height);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow-sm);
}

.header .container {
  max-width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 var(--spacing-lg);
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

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

/* ============================================
   Main Layout
   ============================================ */
.main-container {
  display: flex;
  height: calc(100vh - var(--header-height));
  overflow: hidden;
}

/* ============================================
   Sidebar
   ============================================ */
.sidebar {
  width: var(--sidebar-width);
  background-color: var(--bg-primary);
  border-right: 1px solid var(--border-color);
  overflow-y: auto;
  padding: var(--spacing-lg);
}

.sidebar-content {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xl);
}

.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--spacing-md);
}

.section-header h2 {
  font-size: 0.875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-secondary);
}

.lists-menu {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xs);
}

.list-item {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  position: relative;
}

.list-item:hover {
  background-color: var(--bg-tertiary);
}

.list-item.active {
  background-color: var(--primary);
  color: white;
}

.list-item.active .list-icon,
.list-item.active .list-name {
  color: white;
}

.list-icon {
  font-size: 1.25rem;
}

.list-name {
  flex: 1;
  font-weight: 500;
}

.task-count {
  background-color: var(--bg-tertiary);
  color: var(--text-secondary);
  padding: 0.125rem 0.5rem;
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 600;
}

.list-item.active .task-count {
  background-color: rgba(255, 255, 255, 0.2);
  color: white;
}

.filters-section {
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--border-color);
}

.filter-group {
  margin-bottom: var(--spacing-md);
}

.filter-label {
  display: block;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
}

.filter-select {
  width: 100%;
  padding: var(--spacing-sm) var(--spacing-md);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-size: 0.875rem;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.filter-select:hover {
  border-color: var(--primary);
}

.filter-select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

/* ============================================
   Content Area
   ============================================ */
.content-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
  padding: var(--spacing-lg);
}

.toolbar {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-lg);
}

.search-box {
  flex: 1;
  position: relative;
  max-width: 500px;
}

.search-input {
  width: 100%;
  padding: var(--spacing-sm) var(--spacing-md) var(--spacing-sm) 2.5rem;
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-size: 0.875rem;
  transition: all var(--transition-fast);
}

.search-input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.search-icon {
  position: absolute;
  left: var(--spacing-md);
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  pointer-events: none;
}

.toolbar-actions {
  display: flex;
  gap: var(--spacing-sm);
}

.tasks-container {
  flex: 1;
  overflow-y: auto;
  background-color: var(--bg-primary);
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-sm);
}

.tasks-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-md);
  border-bottom: 1px solid var(--border-color);
}

.tasks-header h2 {
  font-size: 1.5rem;
  font-weight: 700;
}

.tasks-count {
  color: var(--text-secondary);
  font-size: 0.875rem;
}

.tasks-list {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.empty-state {
  text-align: center;
  padding: var(--spacing-xl) var(--spacing-md);
  color: var(--text-muted);
  display: none;
}

.empty-state.show {
  display: block;
}

.empty-icon {
  font-size: 4rem;
  margin-bottom: var(--spacing-md);
  opacity: 0.5;
}

/* ============================================
   Task Item
   ============================================ */
.task-item {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: var(--spacing-md);
  transition: all var(--transition-base);
  cursor: move;
  position: relative;
}

.task-item:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.task-item.completed {
  opacity: 0.7;
}

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

.task-item.overdue {
  border-left: 4px solid var(--danger);
}

.task-item.priority-high {
  border-left: 4px solid var(--priority-high);
}

.task-item.priority-medium {
  border-left: 4px solid var(--priority-medium);
}

.task-item.priority-low {
  border-left: 4px solid var(--priority-low);
}

.task-header {
  display: flex;
  align-items: flex-start;
  gap: var(--spacing-md);
}

.task-checkbox {
  width: 20px;
  height: 20px;
  cursor: pointer;
  accent-color: var(--primary);
  margin-top: 0.125rem;
}

.task-content {
  flex: 1;
  min-width: 0;
}

.task-title {
  font-weight: 600;
  font-size: 1rem;
  margin-bottom: var(--spacing-xs);
  color: var(--text-primary);
}

.task-description {
  font-size: 0.875rem;
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
  line-height: 1.5;
}

.task-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--spacing-sm);
  font-size: 0.75rem;
  color: var(--text-muted);
}

.task-due-date {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.task-due-date.overdue {
  color: var(--danger);
  font-weight: 600;
}

.priority-badge {
  padding: 0.125rem 0.5rem;
  border-radius: var(--radius-sm);
  font-weight: 600;
  text-transform: uppercase;
  font-size: 0.625rem;
  letter-spacing: 0.05em;
}

.priority-badge.high {
  background-color: rgba(239, 68, 68, 0.1);
  color: var(--priority-high);
}

.priority-badge.medium {
  background-color: rgba(245, 158, 11, 0.1);
  color: var(--priority-medium);
}

.priority-badge.low {
  background-color: rgba(16, 185, 129, 0.1);
  color: var(--priority-low);
}

.task-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-xs);
  margin-top: var(--spacing-sm);
}

.tag {
  background-color: var(--bg-tertiary);
  color: var(--text-secondary);
  padding: 0.125rem 0.5rem;
  border-radius: var(--radius-sm);
  font-size: 0.625rem;
  font-weight: 500;
}

.task-actions {
  display: flex;
  gap: var(--spacing-xs);
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.task-item:hover .task-actions {
  opacity: 1;
}

.subtasks-container {
  margin-top: var(--spacing-sm);
  padding-left: var(--spacing-xl);
  border-left: 2px solid var(--border-color);
}

.subtask-item {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-xs) 0;
  font-size: 0.875rem;
}

.subtask-checkbox {
  width: 16px;
  height: 16px;
  cursor: pointer;
  accent-color: var(--primary);
}

/* ============================================
   Buttons
   ============================================ */
.btn {
  padding: var(--spacing-sm) var(--spacing-lg);
  border: none;
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition-fast);
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-sm);
  white-space: nowrap;
}

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

.btn-primary:hover {
  background-color: var(--primary-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

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

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

.btn-icon {
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--spacing-sm);
  border-radius: var(--radius-md);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
  color: var(--text-primary);
}

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

.btn-small {
  padding: var(--spacing-xs);
  font-size: 0.75rem;
}

.btn-danger {
  background-color: var(--danger);
  color: white;
}

.btn-danger:hover {
  background-color: #dc2626;
}

/* ============================================
   Modals
   ============================================ */
.modal {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.5);
  z-index: 1000;
  align-items: center;
  justify-content: center;
  backdrop-filter: blur(4px);
  animation: fadeIn var(--transition-base);
}

.modal.show {
  display: flex;
}

@keyframes fadeIn {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

.modal-content {
  background-color: var(--bg-primary);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-xl);
  width: 90%;
  max-width: 600px;
  max-height: 90vh;
  overflow-y: auto;
  animation: slideUp var(--transition-base);
}

.modal-small {
  max-width: 400px;
}

.modal-large {
  max-width: 800px;
}

@keyframes slideUp {
  from {
    transform: translateY(20px);
    opacity: 0;
  }
  to {
    transform: translateY(0);
    opacity: 1;
  }
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-lg);
  border-bottom: 1px solid var(--border-color);
}

.modal-header h3 {
  font-size: 1.25rem;
  font-weight: 700;
}

.modal-body {
  padding: var(--spacing-lg);
}

.modal-footer {
  display: flex;
  justify-content: flex-end;
  gap: var(--spacing-sm);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--border-color);
  margin-top: var(--spacing-lg);
}

/* ============================================
   Forms
   ============================================ */
.form-group {
  margin-bottom: var(--spacing-lg);
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--spacing-md);
}

.form-group label {
  display: block;
  font-weight: 600;
  font-size: 0.875rem;
  margin-bottom: var(--spacing-sm);
  color: var(--text-primary);
}

.form-group input[type="text"],
.form-group input[type="datetime-local"],
.form-group textarea,
.form-group select {
  width: 100%;
  padding: var(--spacing-sm) var(--spacing-md);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-size: 0.875rem;
  font-family: inherit;
  transition: all var(--transition-fast);
}

.form-group input:focus,
.form-group textarea:focus,
.form-group select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

.form-group textarea {
  resize: vertical;
  min-height: 80px;
}

.form-group input[type="checkbox"] {
  width: auto;
  margin-right: var(--spacing-sm);
  cursor: pointer;
  accent-color: var(--primary);
}

.recurrence-select {
  margin-top: var(--spacing-sm);
}

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

/* ============================================
   Responsive Design
   ============================================ */
@media (max-width: 768px) {
  .main-container {
    flex-direction: column;
  }

  .sidebar {
    width: 100%;
    height: auto;
    max-height: 300px;
    border-right: none;
    border-bottom: 1px solid var(--border-color);
  }

  .toolbar {
    flex-direction: column;
    align-items: stretch;
  }

  .search-box {
    max-width: 100%;
  }

  .form-row {
    grid-template-columns: 1fr;
  }

  .modal-content {
    width: 95%;
    margin: var(--spacing-md);
  }
}

/* ============================================
   Drag & Drop Styles
   ============================================ */
.task-item.dragging {
  opacity: 0.5;
  transform: rotate(2deg);
}

.task-item.drag-over {
  border-top: 3px solid var(--primary);
}

/* ============================================
   Animations
   ============================================ */
@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateX(-10px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

.task-item {
  animation: slideIn var(--transition-base);
}

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

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

.mt-sm {
  margin-top: var(--spacing-sm);
}

.mb-sm {
  margin-bottom: var(--spacing-sm);
}