@import url('https://fonts.googleapis.com/css?family=Montserrat:300,800&display=swap');

  * {
   box-sizing: border-box; 
  }
  body {
    margin: 0;
    text-align: center;
    font-family: 'Montserrat', sans-serif;
    font-weight: 800;
    font-size: 21px;

  }
  #main {
    display: flex;
    min-height: calc(100vh - 40vh);
  }
  #main > article {
    flex: 1;
  }
  #main > nav, 
  #main > aside {
    flex: 0 0 20vw;
    background: #3d71f5;
  }
  #main > nav {
    order: -1;
  }
  header, footer, article, nav, aside {
    padding: 1em;
  }
  header, footer {
    background: #CDCDCD;
    height: 20vh;
  }