Codebase Browser
chromium
Go to App

chromium/third_party/blink/web_tests/external/wpt/html/rendering/replaced-elements/images/input-image-content.html 

<!DOCTYPE html>
<meta charset="utf-8">
<title>Input type=image with CSS content.</title>
<link rel="author" href="mailto:[email protected]">
<link rel="match"  href="input-image-content-ref.html">

You should see a red dot.<br>
<style>
  input {
    content: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==);
  }
</style>

<input type="image">