如何在CSS中创建功能区形状

https://jsfiddle.net/6HyjZ/

.bookmarkRibbon{
     width:0; 
     height:100px; 
     border-right:50px solid blue;
     border-left:50px solid blue;
     border-bottom:30px solid transparent;
}

<div class="bookmarkRibbon"></div>
.bookmarkRibbon{