.page {
   position: fixed;
   width: 100%;
   height: 100%;
   display: flex;
   flex-direction: column;
   justify-content: center;
   align-items: center;
   top: 0;
   left: 0;
   z-index: 4;
   background: rgba(0, 0, 0, 0.5);
}

.page__image {
   width: 700px;
}

@media screen and (max-width: 900px) {
   .page__image {
      width: calc((100vw - 377px)/(900 - 377) * (700 - 300) + 300px);
   }
}