CSS实现九宫格，细边框

1、html结构

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

2、css布局flex实现

.container {
      display: flex;
      flex-wrap: wrap;
      width: 300px;
}
.container div {
      width: 100px;
      height: 100px;
      box-sizing: border-box;
      border: 1px solid #ccc;
      margin-left: -1px;
      margin-top: -1px;
}

未完待续