    border-left: solid 5px blue;
  }
</style>

<body>
  <div class="grid-container">
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
  </div>
</body>

<div class="col-gap1">
  <div class="col-gap1a"></div>
  <div class="col-gap1b"></div>
  <div class="col-gap1c"></div>
</div>
<div class="col-gap2">