html {
  margin: 10px;
  padding: 10px;
  background: url("cuadricula-transp.png") lightblue;
}

body {
  margin: 10px;
  padding: 10px;
  background: url("cuadricula-transp.png") lightyellow;
  font-family: sans-serif;
  font-weight: bold;
}

h1 {
  margin: 0;
  border: black 2px solid;
}