body{
    font-family: helvetica, sans-serif, serif;
}

#droppable{
    width: 150px;
    height: 150px;
    padding: 0.5em;
    float: left;
    margin: 10px;
}

#draggable, #draggable-nonvalid{
    width: 100px;
    height: 100px;
    padding: 0.5em;
    float: left;
    margin: 10px 10px 10px 0px;
}