.btn-file {
   position: relative;
   overflow: hidden;
}
.btn-file input[type=file] {
   position: absolute;
   top: 0;
   right: 0;
   min-width: 100%;
   min-height: 100%;
   font-size: 100px;
   text-align: right;
   filter: alpha(opacity=0);
   opacity: 0;
   outline: none;
   background: white;
   cursor: inherit;
   display: block;
}