style.css

.sidebar-content .site-main,
.content-sidebar .site-main {
  float: left;
  width: 65.75%;
}

.sidebar-content .sidebar-primary,
.content-sidebar .sidebar-primary {
  float: left;
  width: 28.68%;
}

.sidebar-content .site-main,
.content-sidebar .sidebar-primary {
  float: right;
}

@supports( grid-area: auto ) {
  
  .sidebar-content .site-main,
  .content-sidebar .site-main,
  .sidebar-content .sidebar-primary,
  .content-sidebar .sidebar-primary {
    float: none;
    width: 100%;
  }
  
  .content-sidebar .content-area {
    display: grid;
    grid-template-columns: 1fr 335px;
    grid-column-gap: 32px;
  }

  .sidebar-content .content-area {
    grid-template-columns: 335px 1fr;
  }
  
}