body {
  margin: 0;
  padding: 0;
  background-image: url('../img/bg.png');
  background-repeat: repeat;
  background-position: center;
  background-attachment: fixed;
  background-size: auto;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
}

.main-image-container {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
}

.main-image {
  display: block;
  max-width: 100%;
  height: auto;
  width: auto;
}

/* 1200px未満のときのレスポンシブ対応 */
@media (max-width: 1200px) {
  .main-image {
    width: 90%;
  }

  body {
    background-size: 180vw auto;
  }
}