Override this CSS style to define the default(unselect) button's style.
<style type="text/css">
.gk1 .l-btn{
background: #ddd;
}
.gk1 .l-btn-selected{
background: green;
color: #fff;
}
.gk2 .l-btn{
background: #fafafa;
}
.gk2 .l-btn-selected{
background: red;
color: #fff;
}
</style>