:root {
  --bg: #f0f2f5;
  --surface: #ffffff;
  --surface-hover: #f8f9fa;
  --text-primary: #1a1a2e;
  --text-secondary: #6b7280;
  --text-muted: #9ca3af;
  --border: #e5e7eb;
  --border-light: #f3f4f6;
  --primary: #4f46e5;
  --primary-light: #eef2ff;
  --primary-hover: #4338ca;
  --danger: #ef4444;
  --danger-light: #fef2f2;
  --danger-hover: #dc2626;
  --success: #10b981;
  --success-light: #ecfdf5;
  --warning: #f59e0b;
  --warning-light: #fffbeb;
  --priority-low: #10b981;
  --priority-medium: #f59e0b;
  --priority-high: #ef4444;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.1), 0 1px 2px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
  --radius: 8px;
  --radius-lg: 12px;
  --transition: 200ms ease;
}

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

body {
  font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background-color: var(--bg);
  color: var(--text-primary);
  line-height: 1.5;
  min-height: 100vh;
}

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

/* Header */
.app-header {
  background-color: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 12px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: sticky;
  top: 0;
  z-index: 10;
  box-shadow: var(--shadow-sm);
}

.header-left {
  display: flex;
  align-items: center;
  gap: 10px;
}

.logo-icon {
  width: 28px;
  height: 28px;
  color: var(--primary);
}

.app-header h1 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.header-right {
  display: flex;
  align-items: center;
}

.search-wrapper {
  position: relative;
}

.search-icon {
  position: absolute;
  left: 10px;
  top: 50%;
  transform: translateY(-50%);
  width: 16px;
  height: 16px;
  color: var(--text-muted);
  pointer-events: none;
}

.search-input {
  font-family: inherit;
  font-size: 0.875rem;
  padding: 8px 12px 8px 34px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg);
  color: var(--text-primary);
  width: 240px;
  transition: border-color var(--transition), box-shadow var(--transition);
  outline: none;
}

.search-input::placeholder {
  color: var(--text-muted);
}

.search-input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}

/* Main Content */
.app-main {
  flex: 1;
  max-width: 960px;
  width: 100%;
  margin: 0 auto;
  padding: 24px;
}

/* Toolbar */
.toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 24px;
  gap: 12px;
}

.filter-tabs {
  display: flex;
  gap: 4px;
  background: var(--surface);
  padding: 4px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
}

.filter-btn {
  font-family: inherit;
  font-size: 0.8125rem;
  font-weight: 500;
  padding: 6px 14px;
  border: none;
  border-radius: 6px;
  background: transparent;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
}

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

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

.add-btn {
  font-family: inherit;
  font-size: 0.875rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 8px 18px;
  border: none;
  border-radius: var(--radius);
  background: var(--primary);
  color: white;
  cursor: pointer;
  transition: background var(--transition), transform var(--transition), box-shadow var(--transition);
  box-shadow: var(--shadow-sm);
}

.add-btn svg {
  width: 16px;
  height: 16px;
}

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

.add-btn:active {
  transform: translateY(0);
}

/* Tasks Grid */
.tasks-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}

/* Task Card */
.task-card {
  background: var(--surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  transition: box-shadow var(--transition), transform var(--transition), border-color var(--transition);
  position: relative;
  animation: fadeIn 300ms ease;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.task-card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
  border-color: var(--primary);
}

.task-card.completed {
  opacity: 0.65;
}

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

.task-card-header {
  display: flex;
  align-items: flex-start;
  gap: 12px;
}

.task-checkbox {
  appearance: none;
  -webkit-appearance: none;
  width: 20px;
  height: 20px;
  min-width: 20px;
  border: 2px solid var(--border);
  border-radius: 50%;
  cursor: pointer;
  transition: all var(--transition);
  position: relative;
  margin-top: 2px;
}

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

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

.task-checkbox:checked::after {
  content: "";
  position: absolute;
  top: 3px;
  left: 6px;
  width: 4px;
  height: 8px;
  border: solid white;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}

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

.task-title {
  font-size: 0.9375rem;
  font-weight: 600;
  color: var(--text-primary);
  word-wrap: break-word;
  line-height: 1.4;
}

.task-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-top: 4px;
  flex-wrap: wrap;
}

.task-date {
  font-size: 0.75rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 4px;
}

.task-date svg {
  width: 12px;
  height: 12px;
}

.priority-badge {
  font-size: 0.6875rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 2px 8px;
  border-radius: 9999px;
}

.priority-badge.low {
  color: var(--priority-low);
  background: var(--success-light);
}

.priority-badge.medium {
  color: var(--priority-medium);
  background: var(--warning-light);
}

.priority-badge.high {
  color: var(--priority-high);
  background: var(--danger-light);
}

.task-description {
  font-size: 0.8125rem;
  color: var(--text-secondary);
  line-height: 1.6;
  word-wrap: break-word;
  white-space: pre-wrap;
}

.task-actions {
  display: flex;
  gap: 4px;
  margin-top: auto;
  padding-top: 8px;
  border-top: 1px solid var(--border-light);
}

.task-action-btn {
  font-family: inherit;
  font-size: 0.75rem;
  font-weight: 500;
  padding: 6px 12px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
  display: flex;
  align-items: center;
  gap: 4px;
}

.task-action-btn svg {
  width: 13px;
  height: 13px;
}

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

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

/* Empty State */
.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 80px 24px;
  text-align: center;
}

.empty-icon {
  width: 64px;
  height: 64px;
  color: var(--text-muted);
  margin-bottom: 16px;
  opacity: 0.5;
}

.empty-state h3 {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: 4px;
}

.empty-state p {
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* Form Overlay */
.form-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.3);
  backdrop-filter: blur(4px);
  z-index: 40;
  transition: opacity 300ms ease;
}

/* Slide-in Form Panel */
.task-form-panel {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  width: 440px;
  max-width: 100vw;
  background: var(--surface);
  box-shadow: var(--shadow-lg);
  z-index: 50;
  transform: translateX(100%);
  transition: transform 300ms cubic-bezier(0.4, 0, 0.2, 1);
  display: flex;
  flex-direction: column;
}

.task-form-panel.open {
  transform: translateX(0);
}

.task-form-panel form {
  display: flex;
  flex-direction: column;
  height: 100%;
}

.form-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  border-bottom: 1px solid var(--border);
}

.form-header h2 {
  font-size: 1.125rem;
  font-weight: 600;
}

.icon-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border: none;
  border-radius: var(--radius);
  background: transparent;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition);
}

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

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

.form-body {
  flex: 1;
  overflow-y: auto;
  padding: 24px;
  display: flex;
  flex-direction: column;
  gap: 20px;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.form-group.flex-grow {
  flex: 1;
}

.form-group.flex-grow textarea {
  flex: 1;
  min-height: 120px;
  resize: vertical;
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

.form-label {
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--text-primary);
}

.form-control {
  font-family: inherit;
  font-size: 0.875rem;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text-primary);
  transition: border-color var(--transition), box-shadow var(--transition);
  outline: none;
}

.form-control::placeholder {
  color: var(--text-muted);
}

.form-control:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}

select.form-control {
  cursor: pointer;
}

.form-footer {
  display: flex;
  justify-content: flex-end;
  gap: 8px;
  padding: 16px 24px;
  border-top: 1px solid var(--border);
}

/* Buttons */
.btn {
  font-family: inherit;
  font-size: 0.875rem;
  font-weight: 500;
  padding: 8px 20px;
  border: none;
  border-radius: var(--radius);
  cursor: pointer;
  transition: all var(--transition);
}

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

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

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

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

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

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

/* Dialog */
dialog {
  border: none;
  border-radius: var(--radius-lg);
  padding: 0;
  box-shadow: var(--shadow-lg);
  max-width: 400px;
  width: 90%;
}

dialog::backdrop {
  background: rgba(0, 0, 0, 0.4);
  backdrop-filter: blur(4px);
}

.dialog-content {
  padding: 32px;
  text-align: center;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
}

.dialog-icon {
  width: 40px;
  height: 40px;
  color: var(--warning);
  margin-bottom: 4px;
}

#confirm-delete-dialog .dialog-icon {
  color: var(--danger);
}

.dialog-content h3 {
  font-size: 1.0625rem;
  font-weight: 600;
}

.dialog-content p {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

.dialog-actions {
  display: flex;
  gap: 8px;
  margin-top: 16px;
}

.hidden {
  display: none !important;
}

/* Responsive */
@media (max-width: 640px) {
  .app-header {
    padding: 12px 16px;
    flex-wrap: wrap;
    gap: 12px;
  }

  .search-wrapper {
    width: 100%;
    order: 3;
  }

  .search-input {
    width: 100%;
  }

  .app-main {
    padding: 16px;
  }

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

  .filter-tabs {
    justify-content: center;
  }

  .add-btn {
    justify-content: center;
  }

  .tasks-grid {
    grid-template-columns: 1fr;
  }

  .task-form-panel {
    width: 100vw;
  }

  .form-row {
    grid-template-columns: 1fr;
    gap: 20px;
  }
}

@media (min-width: 641px) and (max-width: 900px) {
  .tasks-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}