<div id="box1">
<p>Ciao mondo!!!</p>
</div>

<div id="box2">
<p>Ciao Mondo 2</p>
</div> 

#box1{
  width: 600px;
  height: 300px;
  background-color: #0097A7;
}
#box1 p{
  background-color: #4DD0E1;
  width: 50%;
}

#box2{
  width: 600px;
  height: 300px;
  background-color: #FF8F00;
}
#box2 p{
  background-color: #FFCA28;
  width: 50vw;
}