console 命令行工具 X clear

console

<div class="box"></div>

* {
     padding: 0;
     margin: 0;
 }

 html,
 body {
     width: 100%;
     height: 100%;
 }

 body {
     position: relative;
 }

 .box {
     position: absolute;
     left: 0;
     top: 0;
     right: 0;
     bottom: 0;
     background: red;
     box-sizing: border-box;
     width: 50%;
     padding-bottom: 50%;
     height: 0;
     margin: auto;
 }