body {
  background-color: #dcdcdc;
  background-image: url("BG/BG_SPRING.webp");
  background-repeat: no-repeat;
  background-position: center top;
  background-attachment: fixed;
  background-size: cover;

  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

#header {
  width: 900px;

  margin: 18px auto 0 auto;

  background: #ffffff;
  border: 1px solid #aaaaaa;

  padding: 12px 14px 10px 14px;
}

#title {
  font-size: 28px;
  font-weight: bold;

  margin-bottom: 4px;
}

#description {
  font-size: 12px;
  color: #555555;

  margin-bottom: 10px;

  line-height: 1.4;
}

#nav {
  font-size: 12px;

  border-top: 1px solid #dddddd;

  padding-top: 6px;
}

#nav a {
  color: #0000ee;
}

#nav a:visited {
  color: #551a8b;
}

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

#content {
  background: #ffffff;
  border: 1px solid #aaaaaa;

  width: 900px;

  margin: 10px auto 18px auto;

  padding: 14px;
}
h1 {
  font-size: 24px;
  border-bottom: 1px solid #cccccc;
  margin-top: 0;
}

h2 {
  font-size: 19px;
  border-bottom: 1px solid #dddddd;
}

img {
  max-width: 100%;
  height: auto;
}

iframe {
  max-width: 100%;
}

.footer {
  border-top: 1px solid #cccccc;
  margin-top: 25px;
  padding-top: 8px;
  font-size: 11px;
  color: #555555;
}

.side_img {
  float: right;

  margin-left: 16px;
  margin-bottom: 10px;

  border: 1px solid #999999;
}

.side_img img {
  display: block;
}

.clear {
  clear: both;
}

/* -------------------- MOBILE -------------------- */

@media screen and (max-width: 980px) {

  #header,
  #content {
    width: auto;
    margin-left: 10px;
    margin-right: 10px;
  }

  #title {
    font-size: 22px;
  }

  #description {
    font-size: 11px;
  }

  #nav {
    line-height: 1.8;
  }

  iframe {
    width: 100%;
    height: auto;
    aspect-ratio: 4 / 3;
  }

  img {
    max-width: 100%;
    height: auto;
  }
}