html {
    margin: 0;
    padding: 0;
    background: url(../Images/FondPerrenot.png) no-repeat; 
    background-size: 100%;
    background-position: top;
    min-width:800px;
    min-height:290px;
}

body {
    color: #333;
    font-size: .85em;
    font-family: "Segoe UI", Verdana, Helvetica, Sans-Serif;
    margin: 0;
    padding: 0;
}

@media (max-width: 800px) {

    .bg {
        background-size: 800px 290px; /* Force the image to its minimum width */
    }

}