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

:root {
  --primary: #4f46e5;
  --primary-hover: #4338ca;
  --secondary: #64748b;
  --success: #22c55e;
  --danger: #ef4444;
  --bg: #f8fafc;
  --surface: #ffffff;
  --text: #1e293b;
  --text-muted: #64748b;
  --border: #e2e8f0;
  --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --radius: 8px;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  padding: 2rem 1rem;
}

.app-container {
  width: 100%;
  max-width: 600px;
}

header {
  background: var(--surface);
  padding: 1.5rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  margin-bottom: 1.5rem;
}

header h1 {
  font-size: 1.5rem;
  margin-bottom: 1rem;
  text-align: center;
}

.sync-status {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
  font-size: 0.875rem;
  color: var(--text-muted);
}

.status-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--secondary);
}

.status-dot.online {
  background: var(--success);
}

.status-dot.offline {
  background: var(--secondary);
}

.sync-controls {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
}

.toggle {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  cursor: pointer;
}

.toggle input {
  display: none;
}

.toggle-slider {
  width: 40px;
  height: 20px;
  background: var(--border);
  border-radius: 10px;
  position: relative;
  transition: background 0.3s;
}

.toggle-slider::after {
  content: '';
  position: absolute;
  width: 16px;
  height: 16px;
  background: white;
  border-radius: 50%;
  top: 2px;
  left: 2px;
  transition: transform 0.3s;
}

.toggle input:checked + .toggle-slider {
  background: var(--primary);
}

.toggle input:checked + .toggle-slider::after {
  transform: translateX(20px);
}

.toggle input:disabled + .toggle-slider {
  opacity: 0.5;
  cursor: not-allowed;
}

.btn {
  padding: 0.5rem 1rem;
  border: none;
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 500;
  transition: all 0.2s;
}

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

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

.btn-primary:hover:not(:disabled) {
  background: var(--primary-hover);
}

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

.btn-secondary:hover:not(:disabled) {
  background: #475569;
}

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

.btn-text {
  background: none;
  color: var(--text-muted);
  padding: 0.25rem 0.5rem;
}

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

main {
  background: var(--surface);
  padding: 1.5rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

#task-form {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

#task-input {
  flex: 1;
  padding: 0.75rem 1rem;
  border: 2px solid var(--border);
  border-radius: var(--radius);
  font-size: 1rem;
  transition: border-color 0.2s;
}

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

.filters {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

.filter-btn {
  flex: 1;
  padding: 0.5rem;
  border: 2px solid var(--border);
  background: white;
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 0.875rem;
  transition: all 0.2s;
}

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

.filter-btn:hover:not(.active) {
  border-color: var(--primary);
}

#task-list {
  list-style: none;
  margin-bottom: 1rem;
}

.task-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem;
  border-bottom: 1px solid var(--border);
  animation: slideIn 0.3s ease;
}

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

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

.task-checkbox {
  width: 20px;
  height: 20px;
  cursor: pointer;
}

.task-text {
  flex: 1;
  font-size: 1rem;
}

.task-delete {
  background: none;
  border: none;
  color: var(--text-muted);
  cursor: pointer;
  font-size: 1.25rem;
  padding: 0.25rem;
  border-radius: 4px;
  transition: all 0.2s;
}

.task-delete:hover {
  color: var(--danger);
  background: #fee2e2;
}

.task-stats {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
  font-size: 0.875rem;
  color: var(--text-muted);
}

#toast-container {
  position: fixed;
  bottom: 1rem;
  right: 1rem;
  z-index: 1000;
}

.toast {
  background: var(--surface);
  padding: 0.75rem 1rem;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  margin-top: 0.5rem;
  animation: slideInRight 0.3s ease;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.toast.success {
  border-left: 4px solid var(--success);
}

.toast.error {
  border-left: 4px solid var(--danger);
}

.toast.info {
  border-left: 4px solid var(--primary);
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideInRight {
  from {
    opacity: 0;
    transform: translateX(100%);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@media (max-width: 480px) {
  body {
    padding: 1rem 0.5rem;
  }

  header, main {
    padding: 1rem;
  }

  #task-form {
    flex-direction: column;
  }

  .filters {
    flex-direction: column;
  }

  .task-stats {
    flex-direction: column;
    gap: 0.5rem;
  }
}