@media (min-width: 1200px) {
  /* The main content area */
  .container .row main#main {
    flex: 0 0 63%; /* Equivalent to 10 columns */
    max-width: 63%;
  }

  /* The sidebar/TOC area */
  .container .row aside#sidebar {
    flex: 0 0 37%; /* Equivalent to 2 columns */
    max-width: 37%;
  }
}