* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  background: #eee;
  display: flex;
  flex-direction: column;
  height: 100%;
}

header, footer { 
  flex: none; 
}

main {
  display: flex;
  flex: 1 0 auto;
}