.fond-normal {
    background-color: white;
}

.fond-video {
    background-color: black;
}

#ytb-box {
    position: absolute;
    z-index: 10;
    top: 100px;
    width: 960px;
    min-height: 300px;
    max-height: 800px;
    height: auto;
    overflow: auto;
}

#ytb-video {
    width: 100%;
    height: 500px;
}

#viewer {
    width: 100%;
}

@media only screen and (min-width:960px){
    #ytb-box {left: calc( (100% - 960px)/ 2 );}
}