body{
    margin: auto;
    background-color: white;
    height: 500px; 
    font-family: Arial ; 
}
nav{
    display: flex;
    width: 800px;
    margin: auto;
    justify-content: center;
}
a{
    margin: 10px;
    padding: 7px;
    color: white;
    text-transform: uppercase;
    border-radius: 4px;
    text-decoration: none;
}

a:hover{
    text-decoration: underline;
    color:black;
}
#aa{
    color: #3dd0ac;
    background-color:white;
}
.titre{
    margin-top: 350px;
    font-size: 45px;
    text-transform: uppercase;
    color:  white ;
    text-align: center;
}
header{
    background-image: url(tree.png);
    background-size: 400px;
    background-repeat: no-repeat;
    background-color:#3dd0ac;
    height: 500px;   
    width: 100%;
    box-shadow: 0 0 20px rgba(0,0,0,.2)
}
section{
    margin: auto;
}
h1{

    font-size: 45px;
    text-align: center;
    letter-spacing: 4px;
}
p{
    margin: auto ;
    width: 800px;
}

img,iframe{
    display: block;
    margin: auto;
}
footer{
    display: block;
    padding-top: 15px;
    color: white;
    background-color: #3dd0ac;
    height: 40px;
    text-align: center;
    box-shadow: 0 0 20px rgba(0,0,0,.2)
}