A dead-simple, very basic flexbox based grid, inspired by Glen Madderns talk on CSSConfBP 2016.

flexbox-grid.scss

//Just for the demo
body {
  background: #fafafa;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  color: #333;
}

.row {
  display: flex;
  //min-height set for only the demo
  min-height: 300px;
  padding: 1rem;

  * {
    //background color for the demo
    background-color: lightgreen;
    padding: 0.5rem;
    flex-grow: 1;
  }

  * + * {
    margin-left: 1rem;
  }

  aside {
    flex: 0 0 30%;
  }
}

Here is the link to the slides of the talk.