div{
    width: 300px;
    height: 100px;
    border: 5px dashed #333;
    padding: 10px;
    margin: 10px auto;
    background-color : RGBa(255, 255, 255, 0.2);
}

#ex1, #ex2, #ex3, #ex4{
    background-image: url("../images/smile.jpg");
    background-size: 50px;
   background-repeat: no-repeat; /* une fois*/
}
#ex1{
    background-origin: border-box;
    background-position : top;
}
#ex2{
    background-origin: content-box;
    background-position : top;
}
#ex3{
    background-origin: border-box;
    background-position : top right;
}
#ex4{
    background-origin: border-box;
    background-position : bottom 20px right 100px;
}