body {
  font-family: sans-serif;
  text-align: center;
  padding-top: 5px;
}

/* ▼ ヘッダーナビ */
.nav {
  background: #ffffff;
  padding: 10px 0;
  font-size: 14px;
  border-bottom: 1px solid #ccc;
}

.nav a {
  margin: 0 10px;
  text-decoration: none;
  color: black;
}

.nav a:hover {
  text-decoration: underline;
}

h1 {
  font-size: 40px;
  margin-bottom: 20px;
}

/* ▼カード2枚横並び */
.card-row {
  display: flex;
  justify-content: center;
  gap: 40px;
  margin: 20px auto;
  max-width: 900px;
}

/* ▼練習カード/テストカード */
.card {
  width: 300px;
  background: #f9f9f9;
  padding: 20px;
  border-radius: 12px;
  border: 2px solid #ddd;
}

.card-title {
  font-size: 22px;
  font-weight: bold;
  margin-bottom: 15px;
  color: #00796b;
}

#counter {
  font-size: 14px;
  margin-top: 15px;
  color: #333;
}

/* ▼ボタン */
.btn {
  display: block;
  width: 240px;
  padding: 15px;
  margin: 6px auto;
  border: 2px solid #ccc;
  border-radius: 10px;
  background: #fff;
  font-size: 20px;
  text-decoration: none;
  color: black;
  text-align: center;
}

.btn:hover {
  background: yellow;
}

/* ▼下の文章カード（既存） */
.content-card {
  max-width: 900px;
  margin: 40px auto;
  background: white;
  padding: 40px;
  border-radius: 12px;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
  text-align: left;
}

.content-card h2 {
  font-size: 28px;
  color: #00796b;
  text-align: center;
  margin-bottom: 30px;
  border-bottom: 3px solid #00796b;
  padding-bottom: 15px;
}

.content-card h3 {
  font-size: 24px;
  color: #00796b;
  margin-top: 35px;
  margin-bottom: 20px;
  padding-left: 10px;
  border-left: 5px solid #00796b;
}

.content-card h4 {
  font-size: 20px;
  color: #333;
  margin-top: 25px;
  margin-bottom: 15px;
  font-weight: bold;
}

.content-card section {
  margin-bottom: 40px;
}

.content-card p {
  font-size: 16px;
  line-height: 1.8;
  color: #333;
  margin-bottom: 15px;
  text-align: justify;
}

/* レスポンシブ対応 */
@media (max-width: 768px) {
  .card-row {
    flex-direction: column;
    align-items: center;
  }
  .content-card {
    padding: 20px;
    margin: 20px 10px;
  }
}

/* TOPに戻るボタン */
.back-to-top {
  text-align: center;
  margin-top: 40px;
  padding-top: 30px;
  border-top: 2px solid #e0e0e0;
}

.back-to-top a {
  display: inline-block;
  padding: 12px 30px;
  background: #00796b;
  color: white;
  text-decoration: none;
  border-radius: 8px;
  font-size: 16px;
  font-weight: bold;
  transition: all 0.3s;
}

.back-to-top a:hover {
  background: #005a4d;
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

/* スムーズスクロール */
html {
  scroll-behavior: smooth;
}