* {
  box-sizing:border-box;
} 


body {
  margin: 0;
}

h1 {
  text-align:center;
  padding:25px;
  background-color:grey;
  margin:0px;
}

nav {
  height:50px;
  background-color:dimgrey;
}

aside {
  width:25%;
  
  float:left;
  padding: 10px;
}

section {
  width: 25%;
 
   float:left;
   padding: 10px;
}

article {
 width: 50%;

  float:left;
  padding: 10px;
}

h2 {
  display:block;
  clear:both;
  text-align:center;
  padding:25px;
  background-color:grey;
  margin:0px;
}