insert-image.css

:root {
  --background-color: #ccc;
}

html, body {
  heigth: 100%;
  weight: 100%;
  padding: 0;
  margin: 0;
  background: var(--background-color);
}

.insert-image {
  width: 100%;
  height: 100%;
  background: url('data:image/svg+xml,\
    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">\
        <circle r="15" cx="50" cy="50" fill="yellow" />\
    </svg>');
  background-size: 100px 100px;
}