html, body {
  height: 100%;
}
body {
  display: flex;
  flex-direction: column;
}
.content {
  flex: 1 0 auto;
}

footer{
  flex-shrink: 0;
  height: 62px;
  padding: 8px;
  margin-top: 8px;
  color:#ffffff;
  background-color:#EE6E73;
  text-align: center;
}
article#columna-principal{
  float:left;
  width:65%;
}
aside#costadet{
  float:right;
  width:30%;
  margin-top: 20px;
}