body {
    margin: 0;  
    
    
    }
    header {
        height: 500px;
        background-color: #3dd0ac;
        background-image: url(tree.png);
        background-repeat: no-repeat;
        background-position: left bottom;
    }
    nav {
        width:  800px;
        padding: auto;
        margin: auto;
        padding-top: 10px;
    
    }
    
    
    ol {
        display: flex;
    
        margin: 0;
    
    
      }
    li {
        display: inline;
        margin: 0 30px;
    }
    
    
    nav ol li a {
        text-transform: uppercase;
        color: white;
        text-decoration: none;
        
    }
    
    ol li a:hover {
        text-transform: uppercase;
        color: black;
        text-decoration: underline;
    }
    
    ol li a:visited {
        text-transform: uppercase;
        color: black;
        text-decoration: underline;
    }
    
    ol li a.actif {
        background-color: #fff;
        padding: 5px;
        color:#3dd0ac;
        border-radius: 5px;
    }
    
    .titre {
        position: relative;
        top: 350px;
        text-transform: uppercase;
        font-size: 45px;
        color: white;
        text-align: center;
    }
    
    section {
        margin-bottom: 10px;
        width: 760px;
        margin-left: auto;
        margin-right: auto;
        
        
    }
    
    h1 {
        text-align: center;
    }
    section h1 {
        font-size: 45px;
        padding: 4px 4px 4px 4px
    }
    section p {
        margin-bottom: 10px;
        margin-bottom: 10px;
    }
    
    footer {
        margin-bottom: 10Ppx;
        height: 40px;
        background-color: #3dd0ac;
        box-shadow: 0 0 20px rgba(0,0,0,.2);
        text-align: center;
        color: white;
        display: flex;
      justify-content: center;
      align-items: center;
      text-align: center;
        
    }
    
    footer span {
        text-align: center;
        
    }