.div-left, .div-right {
   
    padding: 1em;
    position: relative;
    
}

.emisor {

    position: absolute;
    padding: 4px;
    width: 30px;
    height: 30px;
    top: 50%;
    transform: translatey(-50%);
    right: -20px;
    border: solid 1px;
    background-color: #fff;

}

.receptor {

    position: absolute;
    padding: 4px;
    width: 30px;
    height: 30px;
    top: 50%;
    transform: translatey(-50%);
    left: -20px;
    background-color: #fff;

}

.drag-option {

    width: 20px;
    height: 20px;
    cursor: move;

}