*  {box-sizing: border-box; }

body {font-family: Arial, Helvetica, sans-serif;}

header {background-color: rgb(0,102,51);
        padding: 30px ;
        text-align: center;
        font-size: 35px;
        color: navy blue;
}

nav {float: left;
    width: 30%;
    height: 2100px;
    background-color: rgb(102,255,204);
    margin: 0px ;
    padding: 0px ;
    list-style-type: none;}
    
    
nav ul {
    list-style-type: none;
    padding: 0 ;
}
 nav li a {padding: 12px; text-decoration: none; color: black; display: block;}
 li a:hover {background-color: rgb(0,204,102);}

article {
    float: right;
    padding: 20px ;
    width: 70%;
    background-color: rgb(0,204,102);;
    height: 2100px;
}

section::after {
         content: "";
         display: table;
         clear: both;
}

footer {
    background-color:rgb(0,153,255);
    padding: 20px ;
    text-align: center;
    color: white;
}
@media (max-width:600px) {nav, article { width: 100%; height: auto;}
}