*{
box-sizing:border.box;
}

<header>
body{
margin:0;
}

header{
background-color:rgb(90, 57, 57);
text-align:center;
padding:25px;
}

.navbar{
background-color:rgb(67, 133, 70);
height:50px;
}

aside{
width:100%;
float:center;
padding:10px;
}

section{
width:100%;
float:center;
padding:10px;
}


footer{
display:block;
clear:both;
background-color:rgb(216, 13, 13);
text-align:center;
padding:25px;
}