   height: 0px;
    border-bottom: solid 5px red;
  }

  .row-gap1 {
    top: 110.5px;
  }

  .row-gap2 {
    top: 220.5px;
  }

  .col-gap {
    position: absolute;
    top: 3px;
    width: 0px;
    height: 330px;
    border-left: solid 5px blue;
  }

  .col-gap1 {
    left: 110.5px;
  }

  .col-gap2 {
    left: 220.5px;
  }
</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