How to set size of SVG image in :before pseudo-class?

I want to display an image in a CSS :before element.

.withimage:before {
  content: url(path/to/image.svg);
  display: block;
  height: 20px;
  width: 20px;
}

The problem is, the height and width are applied to the element, but the SVG doesn't scale down. How do I apply the sizes to the actual element created by before?

Plnkr example: https://plnkr.co/edit/UgryaObojs6PCU579oGY

You can use svg as background-image:

.withimage:before {
  content: "";
  display:block;
  height:125px;
  width:125px;
  background-size: 125px 125px;
  background-image: url(test.svg);
  background-repeat: no-repeat;
}

Here is example

Also you can try use this one:

.withimage:before {
  content: url("data:image/svg+xml; utf8, <svg.. code here</svg>");
    display:block;
    height:20px;
    width:20px;
}