body {    
    margin-left: auto;
    margin-right: auto;
    background-color: aliceblue;
}
nav{position:fixed;}

footer {
    color: white;
    background-color: black;
    bottom: 0px;
    text-align: center;
    position: fixed;
    width: 100%;
}
footer a {
    text-decoration: none;
    color: white;
}

footer a:hover {
    text-decoration: none;
    color: red;
}

span,
li a {
    color: red !important;
}

img{
    max-height: 600px;
}

#myBtn {
    display: none;
    position: fixed;
    bottom: 30px;
    right: 15px;
    z-index: 99;
    font-size: 18px;
    border: none;
    outline: none;
    background-color: red !important;
    color: white;
    cursor: pointer;
    padding: 15px;
    border-radius: 4px;
}

#myBtn:hover {
    background-color: green !important;
}

.haut-droite{
    z-index: 10000;       /* pour mettre au dessus des autres */
    position: absolute;      /* la fameuse position fixed */ 
    top: 1px;            /* décalage des bords */
    right: 1em;
    padding: .5em;        /* donne de l'air au texte */
}

.dropdown button{
    color: red !important;
    border: none;
}