:root {
  --bg: #f5f7fa;
  --surface: #ffffff;
  --text: #1f2937;
  --muted: #6b7280;
  --accent: #3b82f6;
  --accent-hover: #2563eb;
  --danger: #ef4444;
  --danger-hover: #dc2626;
  --border: #e5e7eb;
  --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--text);
  display: flex;
  justify-content: center;
  align-items: flex-start;
  min-height: 100vh;
  padding: 3rem 1rem;
}

.app {
  width: 100%;
  max-width: 480px;
  background: var(--surface);
  border-radius: 12px;
  box-shadow: var(--shadow);
  padding: 1.5rem;
}

h1 {
  margin: 0 0 1rem;
  font-size: 1.75rem;
  text-align: center;
}

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

.todo-form input {
  flex: 1;
  padding: 0.625rem 0.875rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 1rem;
  outline: none;
  transition: border-color 0.2s;
}

.todo-form input:focus {
  border-color: var(--accent);
}

.todo-form button {
  padding: 0.625rem 1.25rem;
  border: none;
  border-radius: 8px;
  background: var(--accent);
  color: white;
  font-size: 1rem;
  cursor: pointer;
  transition: background 0.2s;
}

.todo-form button:hover {
  background: var(--accent-hover);
}

.todo-list {
  list-style: none;
  margin: 0;
  padding: 0;
}

.todo-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.75rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 0.5rem;
  transition: background 0.2s;
}

.todo-item:hover {
  background: #f9fafb;
}

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

.todo-toggle {
  width: 1.25rem;
  height: 1.25rem;
  flex-shrink: 0;
  cursor: pointer;
}

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

.todo-delete {
  padding: 0.375rem 0.625rem;
  border: none;
  border-radius: 6px;
  background: transparent;
  color: var(--danger);
  font-size: 0.875rem;
  cursor: pointer;
  transition: background 0.2s, color 0.2s;
}

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

.todo-footer {
  margin-top: 1rem;
  text-align: center;
  color: var(--muted);
  font-size: 0.875rem;
}

.empty-state {
  text-align: center;
  color: var(--muted);
  padding: 2rem 0;
}