seahub/frontend/src/css/image-file-view.css

.image-file-view {
  position: relative;
  text-align: center;
}
.image-file-view:before {
    content: ' '; 
    display: inline-block;
    vertical-align: middle;
    height: 100%;
    font-size: 0;
    line-height: 0;
}
#image-view {
    padding: 1px; 
    background: #fff;
    border: 1px solid #eee;
    width: auto;
    height: auto;
    max-width: calc(100% - 4px);
    max-height: calc(100% - 4px);
    font-size: 0;
    line-height: 0;
}
#img-prev,
#img-next {
    position:absolute;
    top:48%;
    text-decoration:none;
    color:#888;
    width:50px;
    height:50px;
    background:#fff;
    border-radius:100%;
    line-height:50px;
}
#img-prev {
    left:15px;
}
#img-next {
    right:15px;
}
#img-prev:hover,
#img-next:hover {
    color:#333;
}