将背景色应用于网格之间的间隙

.container {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr; /* 定义三列网格 */
  grid-template-rows: 1fr 1fr 1fr; /* 定义三行网格 */
  grid-gap: 10px; /* 定义行间隙和列间隙的大小 */
}

<div class="container">
  <div class="item">网格项1</div>
  <div class="item">网格项2</div>
  <div class="item">网格项3</div>
  <div class="item">网格项4</div>
  <div class="item">网格项5</div>
  <div class="item">网格项6</div>
  <div class="item">网格项7</div>
  <div class="item">网格项8</div>
  <div class="item">网格项9</div>
</div>

.item {
  background-color: #f2f2f2;
  padding: 10px;
}