You don't see the text because it is hidden away by moving it off the screen. The CSS to blame is this.
Regarding the background image, you need to explicitly add it to your button. For example, using this CSS (this one is from the flag button):
.qa-form-light-button-flag {
background-image: url(images/icons/flag-white.png);
}
Just override those two attributes (and maybe the padding as well) in the button's CSS class to add some content to the button.