html {
  font-size: 10px;
  box-sizing: border-box;
}
*,
*:before,
*:after {
  box-sizing: border-box;
}
body {
  margin: 0;
  font: 1rem/1.4 "Lato", sans-serif;
  background: #ccc;
}
h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: "Roboto Slab", serif;
  margin: 0;
}
p {
  margin: 1rem 0;
}
.topo {
  font-size: 2.8rem;
  text-align: center;
  background: #333;
  color: #f2f2f2;
  line-height: 2;
}
.principal {
  font-size: calc(1.5rem + 0.2vw);
  background: #f3f1f1;
  color: #333;
  width: 100%;
  max-width: 960px;
  margin: 0 auto;
  padding: 10px 20px;
}
ol li {
  margin-bottom: 1.3rem;
}