body { 
  color: black;
  background: white;
  margin-left: 10%;
  margin-right: 10%;
}

h1 { 
  margin-left: -8%;
}

h2,h3,h4,h5,h6 { 
  margin-left: -4%;
}

div.box {  
  border: solid; 
  border-width: thin; 
  width: 100% 
}

div.black { 
  background: grey;
}

pre { 
  border: solid;
  border-width: thin;
  width: 100%;
  background: lightyellow;
 }