main {
      font-family: "Meiryo UI", sans-serif;
      background: #fffde7;
      color: #333;
      margin: 0;
      padding: 1rem;
    }
    .pop-rivet-howto {
      max-width: 1000px;
      margin: auto;
      background: #fff;
      border-radius: 8px;
      box-shadow: 0 4px 20px rgba(0, 0, 0, 0.1);
      padding: 2rem;
    }
    .pop-rivet-howto h1 {
      background: #fdd835;
      color: #212121;
      text-align: center;
      padding: 1rem;
      font-size: clamp(1.5rem, 0.938rem + 1.8vi, 2.063rem);
      border-radius: 8px;
      font-weight:600;
    }
    .pop-rivet-howto h2 {
      text-align: center;
      font-size: 1.5rem;
      margin-top: 2rem;
      color: #d32f2f;
    }
    .pop-rivet-howto table {
      width: 100%;
      border-collapse: collapse;
      margin: 2rem 0;
    }
    .pop-rivet-howto th,
    .pop-rivet-howto td {
      border: 1px solid #aaa;
      text-align: center;
      padding: 0.5rem;
      font-size: 0.95rem;
    }
    .pop-rivet-howto th {
      background: #ffee58;
    }
    .pop-rivet-howto img {
      max-width: 100%;
      height: auto;
    }
    .pop-rivet-howto .caption {
      text-align: center;
      font-size: 1.1rem;
      color: #f57f17;
      margin-bottom: 1rem;
    }
    .pop-rivet-howto .back-button {
      display: flex;
      justify-content: center;
      margin-top: 2rem;
    }
    .pop-rivet-howto .back-button a {
      background: #d32f2f;
      color: white;
      padding: 0.8em 1.2em;
      text-decoration: none;
      border-radius: 5px;
      font-weight: bold;
    }
    .pop-rivet-howto .back-button a:hover {
      background: #b71c1c;
    }
.pop-rivet-howto section {
    padding: 1.5rem 0;
    border-bottom: 1px dashed #ccc;
}
.pop-rivet-howto p{
    font-size: 1.1rem;
    max-width: 600px;
    margin: 0 auto 1em;
}