Edit in JSFiddle

div#corner-triangle {
  display: block;
  width: 100px;
  height: 100px;
  border-style: solid;
  border-width: 0 200px 200px 0;
  border-color: transparent #da0039 transparent transparent;
  position: fixed;
  top: 0;
  right: 0;
  z-index: 99999;
  color: white;
  text-shadow: 0 0 25px 9px #fff;
  -webkit-filter: drop-shadow(0 1px 9px #000000);
  filter: drop-shadow(0 1px 9px #000000);
}
div#corner-triangle .corner-triangle-text {
  position: relative;
  font-size: 2.1em;
  top: 0;
  right: -90px;
  font-family: sans-serif, "Helvetica Neue", Helvetica, Arial;
  font-weight: 200;
  line-height: 1.1;
  -webkit-transform: rotate(45deg);
  -moz-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  -o-transform: rotate(45deg);
  transform: rotate(45deg);
}
div#corner-triangle .corner-triangle-text span.corner-triangle-firstline {
  margin-left: 29px;
}
div#corner-triangle .corner-triangle-text a {
  color: white;
}
div#corner-triangle .corner-triangle-text a:hover,
div#corner-triangle .corner-triangle-text a:link,
div#corner-triangle .corner-triangle-text a:visited,
div#corner-triangle .corner-triangle-text a:active,
div#corner-triangle .corner-triangle-text a:focus {
  text-decoration: none;
}

<div id="corner-triangle">
	<div class="corner-triangle-text text-capitalize"><a href="http://shop.mimijumi.com/" target="_blank"><span class="corner-triangle-firstline">Free</span><br>Shipping!</a></div>
</div>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus quis leo venenatis nisi rhoncus egestas. Aliquam ac efficitur felis. Suspendisse mattis ac massa ac viverra. Praesent vel sapien ut justo consectetur porttitor. Pellentesque lorem urna, sagittis et tempus ac, commodo at elit. Nam nec sagittis elit. Suspendisse quis varius ipsum. Pellentesque dapibus, massa sed rutrum feugiat, erat odio consectetur mi, eu volutpat risus lacus auctor massa. Aliquam ante tellus, auctor sit amet purus vel, iaculis eleifend justo.</p>

<p>Sed fringilla pulvinar rhoncus. Donec vestibulum et leo nec eleifend. Cras quis eros sit amet erat pretium accumsan. Morbi lacinia tincidunt magna, consectetur luctus massa pellentesque ut. Vivamus consectetur dui ipsum, et molestie nulla mattis ut. Vivamus volutpat nibh sed libero elementum rutrum. Aliquam porta tristique tortor in volutpat. Cras aliquam fermentum orci eu tincidunt. Nullam luctus, odio ac pretium efficitur, diam nisl ultrices lacus, quis fringilla dui neque sit amet lacus. Fusce vitae nibh consectetur, porttitor sapien dapibus, tristique purus. Vestibulum lobortis blandit eleifend. Fusce imperdiet diam sit amet scelerisque mollis. Donec eget lacus purus.</p>

<p>Vestibulum a sem quis enim maximus euismod. Curabitur pharetra felis sapien, et ullamcorper diam efficitur ut. Integer efficitur rutrum dui. Praesent imperdiet nulla et euismod lacinia. Quisque consectetur dui nec purus fringilla aliquam. Donec semper dignissim felis id posuere. Praesent tempor accumsan nunc id imperdiet. Donec porta, ex vel malesuada vulputate, erat dolor tempus purus, vitae tempor libero erat vitae risus. Ut faucibus sodales mauris, et iaculis urna posuere ac.</p>