* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans JP", Arial, sans-serif;
  background: #f3f5f9;
  color: #222;
  line-height: 1.8;
}

.header {
  background: #0b2d4f;
  color: #fff;
  text-align: center;
  padding: 34px 20px 26px;
}

.header h1 {
  margin: 0;
  font-size: 26px;
  font-weight: 700;
}

.nav {
  margin-top: 14px;
}

.nav a {
  color: #fff;
  text-decoration: none;
  margin: 0 10px;
  font-size: 14px;
}

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

.container {
  max-width: 860px;
  margin: 28px auto 40px;
  padding: 0 16px;
}

.card {
  background: #fff;
  border-radius: 18px;
  padding: 24px;
  margin-bottom: 20px;
  box-shadow: 0 4px 15px rgba(0, 0, 0, 0.08);
}

h1, h2, h3 {
  margin-top: 0;
  color: #111827;
}

h1 {
  font-size: 28px;
  margin-bottom: 12px;
}

h2 {
  font-size: 22px;
  margin-bottom: 10px;
}

h3 {
  font-size: 18px;
  margin-bottom: 8px;
}

p {
  margin: 0 0 12px;
  font-size: 16px;
}

ul {
  margin: 8px 0 12px 20px;
  padding: 0;
}

li {
  margin-bottom: 6px;
  font-size: 16px;
}

.note {
  background: #eef5ff;
  border-left: 4px solid #1a73e8;
  border-radius: 10px;
  padding: 14px 16px;
  margin-top: 14px;
}

.btn {
  display: inline-block;
  background: #1a73e8;
  color: #fff;
  text-decoration: none;
  padding: 12px 18px;
  border-radius: 10px;
  margin-top: 10px;
  font-size: 15px;
  font-weight: 700;
}

.btn:hover {
  background: #155cc0;
}

.footer {
  text-align: center;
  font-size: 13px;
  margin-top: 30px;
  padding: 0 16px 30px;
}

.footer a {
  color: #1a73e8;
  text-decoration: none;
  margin: 0 6px;
}

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

.center {
  text-align: center;
}

@media (max-width: 600px) {
  .header h1 {
    font-size: 22px;
  }

  .nav a {
    display: inline-block;
    margin: 4px 8px;
    font-size: 13px;
  }

  .card {
    padding: 20px;
    border-radius: 16px;
  }

  h1 {
    font-size: 24px;
  }

  h2 {
    font-size: 20px;
  }

  h3 {
    font-size: 17px;
  }

  p, li {
    font-size: 15px;
  }

  .btn {
    width: 100%;
    text-align: center;
  }
}

.logo {
  color: #fff;
  text-decoration: none;
}

.logo:hover {
  opacity: 0.8;
}