console 命令行工具 X clear

console

var btn = document.getElementById('btn');
setInterval(function(){
  var color = 'green'?'red':'green';
  btn.style.backgroundColor = color;
},200)

<div class="title">header</div>
<div id="btn"></div>

.title{
  color:blue;
  font-size:20px;
}
#btn{
  width:160px;
  height:40px;
  background:green;
}