I'm using the following code to define a custom button background icon:                  
       <style>
                            .km-root .km-pane .km-view .km-logo {
                                background-image: url(styles/images/icon40.png);
                                background-size: 100% 100%;
                            }
                        </style>

For some reason it only works on android. IOS shows a blank button. Any thoughts?

Also, is there any way to make the icon span the entire button? Or else to set the gray part to transparent?