body {
    background-color: #fff;
    color: #000;
    margin: 0;
    padding: 0;
    font-family: system-ui;
  }
  header, footer {
    background-color: #000;
    color: #fff;
    padding: 1em 0;
  }
  .header-container {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 1em;
  }
  .logo {
    text-align: left;
  }
  nav {
    text-align: center;
    margin-top: 1em;
  }
  nav a {
    color: #fff;
    text-decoration: none;
    padding: 0.5em 1em;
    border-radius: 5px;
    transition: background-color 0.3s;
  }
  nav a:hover {
    background-color: #444;
  }
  main {
    padding: 2em;
  }
  .container {
    max-width: 800px;
    margin: 0 auto;
  }
  /* スライドショー用 */
  .slideshow-container {
    position: relative;
    max-width: 100%;
    margin: auto;
  }
  .slide {
    display: none;
  }
  .slide img {
    width: 100%;
    vertical-align: middle;
  }
  .fade {
    animation: fade 1.5s;
  }
  @keyframes fade {
    from {opacity: 0.4;}
    to {opacity: 1;}
  }
  table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 1em;
  }
  table, th, td {
    border: 1px solid #000;
  }
  th, td {
    padding: 0.5em;
    text-align: left;
  }
  th {
    background-color: #f0f0f0;
  }
  h2 {
    position: relative;
    border-bottom: 5px solid #ddd;
    padding: 10px 0;
    font-family: system-ui;
  }
  h2:before {
    position: absolute;
    left: 0;
    bottom: -5px;
    width: 20%;
    height: 5px;
    content: '';
    background: #27acd9;
  }
  .btn {
    display: inline-block;
    padding: 10px 20px;
    background: #27acd9;
    color: #fff;
    text-decoration: none;
    border-radius: 5px;
  }