body {
  margin: 8px;
  background: #c0c0c0;
  color: #000000;
}

.site-rule {
  max-width: 80%;
}

.guestbook-table,
.message-table {
  width: min(500px, calc(100% - 16px));
  table-layout: fixed;
  margin-right: auto;
  margin-left: auto;
}

input[type="text"],
textarea {
  box-sizing: border-box;
  max-width: 100%;
}

textarea {
  width: 100%;
  resize: vertical;
}

.message-content {
  margin-top: 4px;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
}

#error {
  display: none;
  margin: 20px;
  color: #ff0000;
  text-align: center;
}

.website-field {
  position: absolute;
  left: -10000px;
  width: 1px;
  height: 1px;
  overflow: hidden;
}