:root {
  --bg: #f7f7f7;
  --text: #222;
  --muted: #777;
  --primary: #3a86ff;
  --danger: #e63946;
  --card: #fff;
  --border: #e5e5e5;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  background: var(--bg);
  color: var(--text);
}

.app {
  max-width: 560px;
  margin: 48px auto;
  padding: 24px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  box-shadow: 0 10px 30px rgba(0,0,0,0.06);
}

.title {
  margin: 0 0 16px;
  font-weight: 800;
  letter-spacing: -0.02em;
}

.todo-form {
  display: flex;
  gap: 8px;
  margin-bottom: 16px;
}

.todo-input {
  flex: 1;
  padding: 12px 14px;
  font-size: 16px;
  border: 1px solid var(--border);
  border-radius: 8px;
}

.add-btn {
  padding: 12px 16px;
  font-weight: 600;
  color: white;
  background: var(--primary);
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

#undo-btn {
  padding: 12px 16px;
  font-weight: 600;
  color: white;
  background: var(--primary);
  border: none;
  border-radius: 8px;
  cursor: pointer;
}

.add-btn:disabled { opacity: 0.6; cursor: not-allowed; }

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

.todo-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px;
  border: 1px solid var(--border);
  border-radius: 8px;
  margin-bottom: 10px;
}

.todo-title {
  flex: 1;
}

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

.delete-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--danger);
  border-radius: 6px;
  padding: 6px 8px;
  cursor: pointer;
}

.empty-state {
  color: var(--muted);
  text-align: center;
  margin-top: 16px;
}