console 命令行工具 X clear

console

<div class="contaienr1">
  <div class="box1">
         I dont have the width
    </div>
</div>

.contaienr1 {
  width: 400px;
  height: 400px;
  border: 1px solid red;
  margin: 0 auto;
}

.box1 {
  border: 1px solid green;
  margin-left: -20px;
  margin-right: -20px;
}