.btn { border: none; background-color: inherit; padding: 5px 0px; font-size: 18px; cursor: pointer; display: inline-block; color: darkblue;}
.btn:hover {color: red;}
.a:hover {color: red;}
div{padding:2px;}
* { box-sizing: border-box;} 
body{text-align:center;font-family:Helvetica,Arial,sans-serif; font-size: 14px; background-color: linen;} 
#presentation{background-image: url("fond_warhol.png");width:690px; height: 864px; padding-top:30px; background-color:white;margin:auto;}
div.droite1{text-align:right; padding-top:30px; padding-right:5px; width:50%; float:right;} div.lien{padding:10px; float:right;}
div.gauche{float:left;}
a{font-size:18px;}
b{color:darkred;font-size:18px;} 
span{font-size:18px;}
h1.couleur2{color:gray;padding: 50px;}
@media only screen and (max-width:600px){#presentation{width:100%; background-image: url("fond_warhol2.png"); } #fenetre{width: 100%;} div.gauche{width: 100%;} body{background-image: url("fond_warhol2.png");} div.droite1{width:100%;text-align: center;padding-top:0px;} h1.couleur2{padding:0px;}}