Clean Application — Flexible Box Layout

clap-layout-flex.css

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

body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

#main,
#main > article {
  flex: 1;
}

@media only screen and (min-width: 768px) {
  #main {
    display: flex;
  }

  #main > aside {
    flex: 0 0 20%;
  }

  #main > aside:first-of-type {
    order: -1;
  }
}

URL: https://levelup.gitconnected.com/clean-application-flexible-box-layout-98e439bb7d96