SOURCE

console 命令行工具 X clear

                    
>
console
<div></div>
html,body { /*这里没用*/
                width: 100%;
                height: 100%;
                margin: 0;
                padding: 0;
            }
div {
                width:100px;
                height:100px;
                border-radius:50%;
                background-color: turquoise;
                 /*下面的只是垂直居中而已*/
                margin: 0 auto; 
                position: relative; 
                top: 50%; 
                margin-top: -50px;
}