  .col-gap3 {
    border-left: 2px solid blue;
    left: 324px;
  }

  .col-gap4 {
    border-left: 10px solid blue;
    left: 430px;
  }

  .col-gap5 {
    border-left: 10px solid blue;
    left: 540px;
  }

  .item {
    background: gray;
    opacity: 0.5;
  }
</style>
<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"></