JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.bookmarkRibbon{
     width:0; 
     height:100px; 
     border-right:50px solid blue;
     border-left:50px solid blue;
     border-bottom:30px solid transparent;
     transform: rotate(270deg);
     margin: 0, 0, 0, 50px;
}