#modal-received-body {
  position: relative;
  overflow: hidden;
}
#modal-received-body::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  background: url('../images/game-receive.jpg') center center / cover no-repeat;
  opacity: 0.15;
  pointer-events: none;
  z-index: 0;
}
/* 強調テキストや太字にも適用 */
#modal-received-body, #modal-received-body *, #modal-received-body strong, #modal-received-body b {
  font-size: 1.1rem;
  line-height: 1.6;
}