.product__image.col-lg-8 {
  width: 35% !important;    /* 強制的に画像エリアを狭く */
  min-width: 220px !important;
  box-sizing: border-box !important;
  padding-right: 20px !important;
}

.product__guide.col-lg-4 {
  width: 65% !important;    /* 強制的に商品情報エリアを広く */
  min-width: 320px !important;
  box-sizing: border-box !important;
  padding-left: 20px !important;
}

.main-product-image {
  max-width: 400px !important;
  width: 100% !important;
  height: auto !important;
  display: block !important;
  margin-left: auto !important;
  margin-right: auto !important;
  box-shadow: none !important;
  border: none !important;
}

@media (max-width: 991px) {
  .product__image.col-lg-8,
  .product__guide.col-lg-4 {
    width: 100% !important;
    min-width: unset !important;
    padding: 0 !important;
  }
  .main-product-image {
    max-width: 100% !important;
  }
}