body {
  font-family: "Arial", sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background-color: #f4f4f4;
  margin: 0;
  padding: 20px;
  box-sizing: border-box;
}

.quiz-container {
  background-color: #fff;
  padding: 30px;
  border-radius: 10px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
  width: 100%;
  max-width: 600px;
  text-align: center;
}

h1 {
  color: #333;
  margin-bottom: 25px;
  font-size: 1.8em;
}

#question-area {
  margin-bottom: 25px;
  text-align: left;
}

#question-text {
  font-size: 1.1em;
  color: #555;
  margin-bottom: 20px;
  line-height: 1.6;
}

.options-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 15px;
}

.option-button {
  background-color: #e9e9e9;
  border: 1px solid #ddd;
  padding: 12px 20px;
  border-radius: 8px;
  font-size: 1em;
  cursor: pointer;
  transition: background-color 0.3s ease, border-color 0.3s ease;
  text-align: left;
}

.option-button:hover {
  background-color: #dcdcdc;
  border-color: #c0c0c0;
}

.option-button.selected {
  background-color: #cce0ff;
  border-color: #99c2ff;
}

.option-button.correct {
  background-color: #d4edda;
  border-color: #28a745;
  color: #155724;
}

.option-button.incorrect {
  background-color: #f8d7da;
  border-color: #dc3545;
  color: #721c24;
}

#feedback-area {
  margin-top: 20px;
  font-weight: bold;
  font-size: 1.1em;
  min-height: 25px; /* Ensure space for feedback */
}

.feedback-correct {
  color: #28a745;
}

.feedback-incorrect {
  color: #dc3545;
}

button {
  background-color: #007bff;
  color: white;
  border: none;
  padding: 12px 25px;
  border-radius: 8px;
  font-size: 1.1em;
  cursor: pointer;
  margin-top: 20px;
  transition: background-color 0.3s ease;
}

button:hover {
  background-color: #0056b3;
}

button:disabled {
  background-color: #cccccc;
  cursor: not-allowed;
}

.hidden {
  display: none;
}

#result-area {
  margin-top: 30px;
  font-size: 1.2em;
  color: #333;
}

#result-area p {
  margin-bottom: 20px;
}

@media (min-width: 480px) {
  .options-grid {
    grid-template-columns: 1fr 1fr; /* 2列表示 */
  }
}
/* 省略：前回のstyle.cssの内容はそのまま */

/* ユニット選択部分のスタイル */
.unit-selection {
    margin-bottom: 25px;
    text-align: center;
    padding: 15px;
    background-color: #e3f2fd; /* 薄い青 */
    border-radius: 8px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.unit-selection label {
    font-size: 1.1em;
    color: #1a237e; /* 濃い青 */
    margin-right: 10px;
    font-weight: bold;
}

.unit-selection select {
    padding: 10px 15px;
    border: 1px solid #90caf9; /* 青いボーダー */
    border-radius: 5px;
    font-size: 1em;
    background-color: #ffffff;
    cursor: pointer;
    outline: none;
    transition: border-color 0.3s ease, box-shadow 0.3s ease;
}

.unit-selection select:focus {
    border-color: #2196f3; /* フォーカス時に濃い青 */
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.3); /* フォーカス時に薄い青の影 */
}