*{
    box-sizing: border-box;
}
body{
    margin: 0;
}
header{
    background-color: hsl(0, 0%, 87%);
    text-align: center;
    padding: 25px;

}
.navbar{
    background-color: hsl(0, 0%, 39%);
    height: 50px;   
}
aside{
    width: 20%;
    float: left;
    padding: 10px;
}
section{
    width: 40%;
    float: left;
    padding: 10px;
}
article{
    width: 40%;
    float: left;
    padding: 10px;
}
footer{
    display: block;
    clear: both;
    text-align: center;
    background-color: hsl(0, 0%, 85%);
    padding: 25px;
}
@media screen and (max-width:600px){
    aside,section,article{
        width: 100%;
    }
    
}