Using :before CSS pseudo element to add image to modal

http://caniuse.com/#search=::after

::after and ::before with content are better to use as they're supported in every major browser other than Internet Explorer at least 5 versions back. Internet Explorer has complete support in version 9+ and partial support in version 8.

Is this what you're looking for?

.Modal::after{
  content:url('blackCarrot.png'); /* with class ModalCarrot ??*/
  position:relative; /*or absolute*/
  z-index:100000; /*a number that's more than the modal box*/
  left:-50px;
  top:10px;
}

.ModalCarrot{
   position:absolute;
   left:50%;
   margin-left:-8px;
   top:-16px;
}

If not, can you explain a little better?

or you could use jQuery, like Joshua said:

$(".Modal").before("<img src='blackCarrot.png' class='ModalCarrot' />");

1.this is my answer for your problem.

.ModalCarrot::before {
content:'';
background: url('blackCarrot.png'); /*url of image*/
height: 16px; /*height of image*/
width: 33px;  /*width of image*/
position: absolute;
}

You should use the background attribute to give an image to that element, and I would use ::after instead of before, this way it should be already drawn on top of your element.

.Modal:before{
  content: '';
  background:url('blackCarrot.png');
  width: /* width of the image */;
  height: /* height of the image */;
  display: block;
}