How to create CSS Bookmark ribbon horizontally with text?

You can use the below CSS for creating horizontal bookmark ribbon 

 .bookmarkRibbon {
        width: 105px;
        height: 0;
        border-bottom: 20px solid #045089;
        border-top: 20px solid #045089;
        border-left: 15px solid transparent;
        float: right;
        margin-bottom: 20px;
        font-size: 17px;
        font-weight:700;
        position: absolute;
        right: 0px;
        top: 20px;
    }

HTML

<div class="bookmarkRibbon"><span style="color:white;position: relative;top: -9px;text-align: center;right: -10px;">20% OFF</span></div>

Here is the working fiddle for you to test.

Above answer is perfect, but if you need right-side ribbon without text, then you can have CSS

.cssRibbon{
  border:       50px solid blue;        /* All borders set */
  border-left:  0;                      /* Remove left border */
  border-right: 30px solid transparent; /* Right transparent */
  width:        100px;                  /* Increase element Width */
}

HTML

<div class="cssRibbon"></div>

here is fiddle demo: https://jsfiddle.net/gqvb869t/