nav{
    width: 30%;
    height: 70%;
    float: left;
    position: relative;
    background-image: url(network.jpg);
    background-size: 100%;
}
header{
    width: 100%;
    height: 20%;
    position: relative;
    background-color: green;
}
section{
width: 60%;
height: 70%;
float: left;
}
footer{
    width: 100%;
    height: 10%;
    float: left;
    position: relative;
    background-color: green;
}
aside{
    width: 10%;
    height: 70%;
    float: right;
}
iframe{
    width: 100%;
    height: 100%;
}
body{
    width: 100vw;
    height: 100vh;
    margin: 0 auto;
}
*{
    font-family: "verdana";
    padding:0px ;
    margin:0px ;
}
header h1{
    float: none;
    font-size: 300%;
    font-weight: bold;
    font-style: italic;
    color: goldenrod;
    text-transform: uppercase;
    text-shadow: 5px 5px silver;
    position: relative;
    width: 100%;
    text-align: center;
    top: 50px;
    transform:translateY(0px) ;
}
footer p{
float: none;
text-align: center;
text-decoration: underline;
text-decoration-color: green;
background-image: linear-gradient(pink, yellow);
position: relative;
top: 50%;
transform:translateY(-50%) ;
}
.fond{
    background-color: greenyellow;
}
a{
    background-color: aqua;
    transition: background-color 500ms linear;
}
a:link{
    color: red;
}
a:visited{
      color: darkgreen;
      }
a:hover{
    color: black;
    background-color: white;
}