/* ========================================
   RESET & BASE STYLES
   ======================================== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --primary-color: #6366f1;
  --primary-dark: #4f46e5;
  --secondary-color: #8b5cf6;
  --accent-color: #ec4899;
  --success-color: #10b981;
  --warning-color: #f59e0b;
  --danger-color: #ef4444;
  --text-primary: #1f2937;
  --text-secondary: #6b7280;
  --bg-primary: #ffffff;
  --bg-secondary: #f9fafb;
  --bg-tertiary: #f3f4f6;
  --border-color: #e5e7eb;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
  --shadow-xl: 0 20px 25px rgba(0, 0, 0, 0.15);
  --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
  --text-primary: #f9fafb;
  --text-secondary: #d1d5db;
  --bg-primary: #1f2937;
  --bg-secondary: #111827;
  --bg-tertiary: #374151;
  --border-color: #4b5563;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  color: var(--text-primary);
  background: var(--bg-secondary);
  line-height: 1.6;
  transition: background 0.3s, color 0.3s;
}

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

.nav-container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 20px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--primary-color);
}

.logo i {
  font-size: 1.75rem;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.theme-toggle {
  background: var(--bg-tertiary);
  border: none;
  width: 40px;
  height: 40px;
  border-radius: 10px;
  cursor: pointer;
  color: var(--text-primary);
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
}

.theme-toggle:hover {
  background: var(--primary-color);
  color: white;
  transform: scale(1.05);
}

.back-link {
  background: var(--primary-color);
  color: white;
  padding: 10px 20px;
  border-radius: 10px;
  text-decoration: none;
  font-weight: 600;
  transition: var(--transition);
  display: flex;
  align-items: center;
  gap: 8px;
}

.back-link:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

/* ========================================
   MAIN LAYOUT
   ======================================== */
.main-container {
  max-width: 1400px;
  margin: 0 auto;
  padding: 2rem 20px;
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: 2rem;
}

/* ========================================
   SIDEBAR
   ======================================== */
.sidebar {
  background: var(--bg-primary);
  border-radius: 20px;
  padding: 2rem;
  height: fit-content;
  position: sticky;
  top: 100px;
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-color);
}

.sidebar-header {
  margin-bottom: 2rem;
}

.sidebar-header h2 {
  font-size: 1.75rem;
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.new-task-btn {
  width: 100%;
  padding: 12px;
  background: var(--primary-color);
  color: white;
  border: none;
  border-radius: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
}

.new-task-btn:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.stats {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin-bottom: 2rem;
}

.stat-card {
  background: var(--bg-secondary);
  padding: 1rem;
  border-radius: 12px;
  display: flex;
  align-items: center;
  gap: 1rem;
  transition: var(--transition);
}

.stat-card:hover {
  transform: translateX(5px);
  box-shadow: var(--shadow-md);
}

.stat-icon {
  width: 50px;
  height: 50px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  color: white;
}

.stat-icon.all {
  background: var(--primary-color);
}

.stat-icon.pending {
  background: var(--warning-color);
}

.stat-icon.completed {
  background: var(--success-color);
}

.stat-info {
  flex: 1;
}

.stat-number {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--text-primary);
}

.stat-label {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.filters,
.categories {
  margin-bottom: 2rem;
}

.filters h3,
.categories h3 {
  font-size: 1rem;
  margin-bottom: 1rem;
  color: var(--text-secondary);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.filter-btn,
.category-btn {
  width: 100%;
  padding: 12px;
  background: var(--bg-secondary);
  border: 2px solid transparent;
  border-radius: 10px;
  text-align: left;
  cursor: pointer;
  transition: var(--transition);
  margin-bottom: 0.5rem;
  color: var(--text-primary);
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 10px;
  font-family: inherit;
}

.filter-btn:hover,
.category-btn:hover {
  background: var(--bg-tertiary);
  border-color: var(--border-color);
}

.filter-btn.active,
.category-btn.active {
  background: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
}

/* ========================================
   MAIN CONTENT
   ======================================== */
.main-content {
  background: var(--bg-primary);
  border-radius: 20px;
  padding: 2rem;
  box-shadow: var(--shadow-md);
  border: 1px solid var(--border-color);
}

.content-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: 2rem;
  flex-wrap: wrap;
  gap: 1rem;
}

.content-header h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

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

.header-actions {
  display: flex;
  gap: 0.5rem;
}

.action-btn {
  padding: 10px 16px;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  cursor: pointer;
  transition: var(--transition);
  color: var(--text-primary);
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: inherit;
}

.action-btn:hover {
  background: var(--bg-tertiary);
  border-color: var(--primary-color);
  color: var(--primary-color);
}

/* ========================================
   TASK INPUT
   ======================================== */
.task-input-section {
  margin-bottom: 2rem;
}

.task-input-wrapper {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

#taskInput {
  flex: 1;
  padding: 14px 18px;
  border: 2px solid var(--border-color);
  border-radius: 12px;
  font-size: 1rem;
  background: var(--bg-secondary);
  color: var(--text-primary);
  font-family: inherit;
  transition: var(--transition);
}

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

.add-btn {
  padding: 14px 20px;
  background: var(--primary-color);
  color: white;
  border: none;
  border-radius: 12px;
  cursor: pointer;
  transition: var(--transition);
  font-size: 1.2rem;
}

.add-btn:hover {
  background: var(--primary-dark);
  transform: scale(1.05);
}

.task-options {
  background: var(--bg-secondary);
  padding: 1.5rem;
  border-radius: 12px;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1rem;
  border: 2px solid var(--border-color);
}

.option-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.option-group label {
  font-size: 0.9rem;
  color: var(--text-secondary);
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 8px;
}

.option-group select,
.option-group input[type="date"] {
  padding: 10px;
  border: 1px solid var(--border-color);
  border-radius: 8px;
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: inherit;
  cursor: pointer;
}

.cancel-btn {
  padding: 10px;
  background: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  color: var(--text-primary);
  cursor: pointer;
  transition: var(--transition);
  font-family: inherit;
  font-weight: 500;
}

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

/* ========================================
   TASKS LIST
   ======================================== */
.tasks-container {
  max-height: 600px;
  overflow-y: auto;
}

.tasks-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.empty-state {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--text-secondary);
}

.empty-state i {
  font-size: 4rem;
  margin-bottom: 1rem;
  opacity: 0.5;
}

.empty-state h3 {
  font-size: 1.5rem;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.task-item {
  background: var(--bg-secondary);
  border: 2px solid var(--border-color);
  border-radius: 12px;
  padding: 1.5rem;
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  transition: var(--transition);
  position: relative;
}

.task-item:hover {
  box-shadow: var(--shadow-md);
  border-color: var(--primary-color);
  transform: translateX(5px);
}

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

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

.task-checkbox {
  width: 24px;
  height: 24px;
  border: 2px solid var(--border-color);
  border-radius: 6px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
  flex-shrink: 0;
  margin-top: 2px;
}

.task-checkbox:hover {
  border-color: var(--primary-color);
}

.task-checkbox.completed {
  background: var(--success-color);
  border-color: var(--success-color);
  color: white;
}

.task-content {
  flex: 1;
}

.task-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.5rem;
  flex-wrap: wrap;
}

.task-title {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-primary);
  flex: 1;
}

.task-priority {
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
}

.task-priority.high {
  background: #fee2e2;
  color: #991b1b;
}

.task-priority.medium {
  background: #fef3c7;
  color: #92400e;
}

.task-priority.low {
  background: #d1fae5;
  color: #065f46;
}

.task-category {
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 0.75rem;
  font-weight: 600;
  background: var(--bg-tertiary);
  color: var(--text-secondary);
}

.task-meta {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.task-meta-item {
  display: flex;
  align-items: center;
  gap: 5px;
}

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

.task-actions {
  display: flex;
  gap: 0.5rem;
  flex-shrink: 0;
}

.task-action-btn {
  width: 36px;
  height: 36px;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.task-action-btn:hover {
  transform: scale(1.1);
}

.task-action-btn.edit:hover {
  background: var(--primary-color);
  color: white;
}

.task-action-btn.delete:hover {
  background: var(--danger-color);
  color: white;
}

/* ========================================
   MODAL
   ======================================== */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
  z-index: 1000;
  display: none;
  align-items: center;
  justify-content: center;
  padding: 20px;
}

.modal-overlay.active {
  display: flex;
}

.modal-content {
  background: var(--bg-primary);
  border-radius: 20px;
  width: 100%;
  max-width: 600px;
  max-height: 90vh;
  overflow-y: auto;
  box-shadow: var(--shadow-xl);
}

.modal-header {
  padding: 2rem;
  border-bottom: 1px solid var(--border-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.modal-header h2 {
  font-size: 1.75rem;
  color: var(--text-primary);
}

.close-modal {
  width: 40px;
  height: 40px;
  border: none;
  background: var(--bg-secondary);
  border-radius: 10px;
  cursor: pointer;
  transition: var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-primary);
}

.close-modal:hover {
  background: var(--danger-color);
  color: white;
  transform: rotate(90deg);
}

.modal-body {
  padding: 2rem;
}

.form-group {
  margin-bottom: 1.5rem;
}

.form-group label {
  display: block;
  margin-bottom: 0.5rem;
  font-weight: 600;
  color: var(--text-primary);
}

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 12px;
  border: 2px solid var(--border-color);
  border-radius: 10px;
  background: var(--bg-secondary);
  color: var(--text-primary);
  font-family: inherit;
  font-size: 1rem;
  transition: var(--transition);
}

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

.modal-footer {
  padding: 2rem;
  border-top: 1px solid var(--border-color);
  display: flex;
  justify-content: flex-end;
  gap: 1rem;
}

.btn {
  padding: 12px 24px;
  border: none;
  border-radius: 10px;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  font-family: inherit;
}

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

.btn-primary:hover {
  background: var(--primary-dark);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.btn-secondary {
  background: var(--bg-secondary);
  color: var(--text-primary);
  border: 2px solid var(--border-color);
}

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

/* ========================================
   SORT DROPDOWN
   ======================================== */
.sort-dropdown {
  position: absolute;
  top: 60px;
  right: 20px;
  background: var(--bg-primary);
  border-radius: 12px;
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--border-color);
  z-index: 100;
  min-width: 200px;
  overflow: hidden;
}

.sort-option {
  width: 100%;
  padding: 12px 16px;
  border: none;
  background: transparent;
  text-align: left;
  cursor: pointer;
  transition: var(--transition);
  color: var(--text-primary);
  font-family: inherit;
}

.sort-option:hover {
  background: var(--bg-secondary);
}

/* ========================================
   RESPONSIVE DESIGN
   ======================================== */
@media (max-width: 1024px) {
  .main-container {
    grid-template-columns: 280px 1fr;
  }
}

@media (max-width: 768px) {
  .main-container {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
    margin-bottom: 2rem;
  }

  .content-header {
    flex-direction: column;
  }

  .task-options {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .nav-container {
    flex-wrap: wrap;
  }

  .task-item {
    flex-direction: column;
  }

  .task-actions {
    width: 100%;
    justify-content: flex-end;
  }
}

/* ========================================
   SCROLLBAR STYLING
   ======================================== */
.tasks-container::-webkit-scrollbar,
.modal-content::-webkit-scrollbar {
  width: 8px;
}

.tasks-container::-webkit-scrollbar-track,
.modal-content::-webkit-scrollbar-track {
  background: var(--bg-secondary);
  border-radius: 10px;
}

.tasks-container::-webkit-scrollbar-thumb,
.modal-content::-webkit-scrollbar-thumb {
  background: var(--border-color);
  border-radius: 10px;
}

.tasks-container::-webkit-scrollbar-thumb:hover,
.modal-content::-webkit-scrollbar-thumb:hover {
  background: var(--text-secondary);
}