body {background-color: black;}

.box {
  display: flex;
  align-items: center;
  justify-content: center;
}
.imgwrap {
   width: 100%; /*or whatever you choose*/
   margin: auto;
}
.imgwrap img {
   display: block;
   width: 100%;
   max-width: 800px; /*actual image width*/
   height: auto; /* maintain aspect ratio*/
   margin: auto; /*optional centering of image*/
}