Icons Not Displaying With Custom Theme

I'm using jQuery mobile with a custom theme created on themeroller According to the instructions I have to include in the : Copy

Moreover, jQM is now using SVG icons for platforms that support SVG and normal icons for ones that dont. Icons are added after an element using pseudo selector :after.

Creating custom icons is simple as the CSS below.

.ui-custom-icon:after {
  background-image: url('custom-icon.png');
  background-size: 25px25px; /* dont forget this */
}

Now add .ui-custom-icon to any element.

Demo