Add note to carousel crossfade docs about bg color (#35587)

Fixes #35181

Co-authored-by: Mark Otto <markdotto@gmail.com>
Co-authored-by: Gaël Poupard <ffoodd@users.noreply.github.com>

.cspell.json

@@ -24,6 +24,7 @@
     "Contentful",
     "Cpath",
     "Crossfade",
+    "crossfading",
     "cssgrid",
     "Csvg",
     "Datalists",

site/content/docs/5.1/components/carousel.md

@@ -152,7 +152,7 @@ Add captions to your slides easily with the `.carousel-caption` element within a
 
 ### Crossfade
 
-Add `.carousel-fade` to your carousel to animate slides with a fade transition instead of a slide.
+Add `.carousel-fade` to your carousel to animate slides with a fade transition instead of a slide. Depending on your carousel content (e.g., text only slides), you may want to add `.bg-body` or some custom CSS to the `.carousel-item`s for proper crossfading.
 
 {{< example >}}
 <div id="carouselExampleFade" class="carousel slide carousel-fade" data-bs-ride="carousel">