i.spt-icon {
    background-image: url('../img/admin/tinymce_icon.png');
    background-size: 16px;
    background-repeat: no-repeat;
}

@media
(-webkit-min-device-pixel-ratio: 2),
(min-resolution: 192dpi) {
    i.spt-icon {
	    background-image: url('../img/admin/tinymce_icon@2x.png');
	    background-size: 16px;
	}
}