Using CleanTheme, I developed a simple css to assign an image to a buton:
.button-image-marcel .x-btn-default-small {
background-image: url("../../../../../Artifacts/Resources/tema/bt_open.png");
height:32px;
width:32px;
cursor:pointer;
border:none;
}
It works fine in deployed aplication (see image below), but the image doesn't appear in Designer.
Application

xCP Designer

How can I configure xCP Designer to fix this ?