console 命令行工具 X clear

console

<body>
  <main>
    <h1>Am I centered yet?</h1>
    <p>Center me, please!</p>
  </main>
</body>

body{
  border:2px solid;
  padding:0;
  margin:0;
  height:400px;
  width:700px;
}
main{
  border:1px solid red;
  text-align:center;
  background:gray;
  height;100px;
  width:350px;
  margin:0 auto;
  position:relative;
  top:50%;
  
  margin-top:-50px;
}