.f,.f *{position:fixed;max-width:100%;max-height:100%;top:50%;left:50%}
.f *{transform:translate(-50%,-50%)}
.f{display:none;top:0;left:0;width:100%;height:100%;background:rgba(0,0,0,0.8)}
*:focus+.f{display:block}
img{cursor:pointer}