html, body {
  height: 100%;
  margin: 0;
}
body {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}

#box-plugin header,
#box-plugin footer {
  height: 45px;
  display: flex;
  justify-content: center;
  align-items: center;
}

#box-plugin article {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}