如何在图片上显示“下一步”和“上一步”按钮？

.screen-reader-text {
  clip: rect(1px, 1px, 1px, 1px);
  position: absolute !important;
}

.post-navigation span {
  display: inline-block;
  width: 4.5rem;
  height: 4.5rem;
  background-color: #333;
  background-clip: content-box;
  border: 0.25rem solid transparent;
  border-radius: 50%;
  font-size: 0;
  transition: transform 0.1s;
}

.nav-previous,
.nav-next {
  position: absolute;
  top: 0;
  margin-top: 37.5%;
  width: 4rem;
  height: 4rem;
  transform: translateY(-50%);
  border-radius: 50%;
  font-size: 0;
  outline: 0;
}

.nav-previous,
.nav-next {
  position: absolute;
  top: 0;
  margin-top: 37.5%;
  width: 4rem;
  height: 4rem;
  transform: translateY(-50%);
  border-radius: 50%;
  font-size: 0;
  outline: 0;
}

.nav-previous {
  left: -1rem;
}

.nav-next {
  right: -1rem;
}

.post-navigation span::before,
.post-navigation span::after {
  content: '';
  z-index: 1;
  background-color: #ccc;
  background-size: 1.5rem 1.5rem;
  background-repeat: no-repeat;
  background-position: center center;
  color: #ffffff;
  font-size: 2.5rem;
  line-height: 4rem;
  text-align: center;
  pointer-events: none;
}

.post-navigation span::before {
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 100 100' xmlns='http://www.w3.org/2000/svg'%3E%3Cpolygon points='0,50 80,100 80,0' fill='%23fff'/%3E%3C/svg%3E");
}

.post-navigation span::after {
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 100 100' xmlns='http://www.w3.org/2000/svg'%3E%3Cpolygon points='100,50 20,100 20,0' fill='%23fff'/%3E%3C/svg%3E");
}

<section class="container">
  <div class="photo-template-author">
    <div class="row">
      <div class="col-md-8 col-xs-12 photo--section--image">
        <div class="photo-video-box-shadow">
          <div class="col-md-12 col-xs-12">
            <nav class="navigation post-navigation" role="navigation" aria-label="Post navigation">
              <h2 class="screen-reader-text">Post navigation</h2>
              <div class="nav-links">
                <div class="nav-previous"><a href="#" rel="prev">
                    <div class="nav-text"><span><i class="fa fa-angle-left"></i> Previous</span> </div>
                  </a></div>
                <div class="nav-next"><a href="#" rel="next">
                    <div class="nav-text"><span>Next <i class="fa fa-angle-right"></i></span> </div>
                  </a></div>
              </div>
            </nav>
          </div>
          <img src="https://1.bp.blogspot.com/-Ctv1m-63Q7Q/TozUCb70gQI/AAAAAAAAAfw/UQk-nUN3NHM/s1600/beautiful+nature+scenery-1.jpg" alt="featured-image" class="featured-img img-responsive">
        </div>
      </div>
    </div>
  </div>

</section>