main {
  width: 400px;
  margin: 30px auto;
}

main h1 {
  font-size: 20px;
  font-weight: bold;
  text-align: center;
  padding-bottom: 10px;
  border-bottom: 1px solid #aaa;
}

main h2 {
  font-size: 16px;
}

ul li {
  cursor: pointer;
}

.correct {
  color: green;
}

.incorrect {
  color: red;
}

.correct::after {
  content: "- 正解！";
}

.incorrect::after {
  content: "- 不正解...";
}