blog_theme/partials/post-navigation.hbs

<div class="navigation">
    <div class="navigation-item navigation-previous{{^prev_post}} navigation-empty{{/prev_post}}">
      {{#prev_post}}
        <img class="navigation-image lazyload u-object-fit"
          data-srcset="{{img_url feature_image size="s"}} 400w, {{img_url feature_image size="m"}} 750w, {{img_url feature_image size="l"}} 960w"
          src="data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw=="
          data-sizes="auto"
          alt="{{title}}"
        >
        <span class="navigation-label">{{t 'Previous Post'}}</span>
        <h4 class="navigation-title">{{title}}</h4>
        <a class="u-permalink" href={{url}}></a>
      {{/prev_post}}
    </div>

  {{#next_post}}
    <div class="navigation-item navigation-next{{^next_post}} navigation-empty{{/next_post}}">
      <img class="navigation-image lazyload u-object-fit"
        data-srcset="{{img_url feature_image size="s"}} 400w, {{img_url feature_image size="m"}} 750w, {{img_url feature_image size="l"}} 960w"
        src="data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw=="
        data-sizes="auto"
        alt="{{title}}"
      >
      <span class="navigation-label">{{t 'Next Post'}}</span>
      <h4 class="navigation-title">{{title}}</h4>
      <a class="u-permalink" href={{url}}></a>
    </div>
  {{/next_post}}
</div>