Add bg always white on img to ensure visibility in dark mode

Author: hannahiss

Diff for: site/content/docs/0.3/extend/icons.md

@@ -643,7 +643,9 @@ Remember that you cannot use external images inside interactive elements because
 <button type="button" class="btn btn-icon btn-default" aria-label="Open settings">
   <span class="icon si si-settings" aria-hidden="true"></span>
 </button>
-<img src="/docs/{{< param docs_version >}}/assets/img/heart-recommend.svg" alt="Favorite" width="32" height="32">
+<div class="d-inline-block bg-always-white">
+  <img src="/docs/{{< param docs_version >}}/assets/img/heart-recommend.svg" alt="Favorite" width="32" height="32">
+</div>
 {{< /example >}}
 
 ## Use Solaris icons