Issue with DIV overlay within CSS style, image over image

Question

I have CSS style within HTML. A responsive image grid is produced from SQL images. I am trying to create a bookmark overlay to add as favourite.

I've tried a number of tutorials. Also, have copied the image DIV and changed the Z position to place above the image, but cannot see the overlay image at all.

style sheet:

#gridview {
  text-align:center; 
}
div.image {
  margin: 10px;
  display: inline-block;
  position: relative;
  z-index: 1;
}
div.image img {
  width: 100%;
  height: auto;
  position: relative;
  border: 1px solid #ccc;
  z-index: 1;
}
div.image img:hover {
  box-shadow: 0 5px 5px 0 rgba(0,0,0,0.32), 0 0 0 0px rgba(0,0,0,0.16);
  z-index: 1;
  position: relative;
}
div.bookmark {
  margin: 10px;
  display: inline-block;
  position: absolute;
  z-index: 3;
}
div.bookmark img {
  width: 100%;
  background-image:       url("https://images.justwatch.com/static/compile_jw/assets/ribbon-filled.png");
  height: auto;
  position: absolute;
  z-index: 3;
}
div.bookmark img:hover {
  box-shadow: 0 5px 5px 0 rgba(0,0,0,0.32), 0 0 0 0px rgba(0,0,0,0.16);
  z-index: 3;
  position: absolute;
}
#grid {
  margin-bottom:30px;
}
@media screen and (min-width: 1224px) {
  div.image {
    width: 154px;
  }
}
media screen and (min-width: 1044px) and (max-width: 1224px) {
  div.image {
    width: 154px;
  }
}
@media screen and (min-width: 845px) and (max-width: 1044px) {
  div.image {
    width: 154px;
  }
}

PHP / HTML page:

var tbl_body = "";
for (var i = 0; i < data.length; i++) 
{
  var tbl_row = "";
  var t = i;
  tbl_row += ("<div class='image'><a href='link/" + data[i]+ "'><IMG SRC='link/"+ data[i].poster +"'></a><div class='bookmark'></div> ");
  tbl_row += ("</div>");
  tbl_body += tbl_row 
}
return tbl_body;

The outcome should be the poster image, with overlay of the bookmark image in the top corner of each poster.