SOURCE

<div></div>

html,body { 
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
}
div {
                  width:100px;
                  border:100px solid transparent;
                  border-bottom:100px solid hotpink;
                  margin: 0 auto; /*水平居中*/
                  position: relative; /*脱离文档流*/
                  top: 50%; /*偏移*/
                  margin-top: -100px;
            }