Remove nested CSS from <FileTree> component

[HiDeoo]

What kind of changes does this PR include?

• Changes to Starlight code

Description

This PR prevents a potential warning when using Tailwind CSS with Starlight due to the <FileTree> component containing nested CSS.

How I tested this change:

• Without the changes, run pnpm dev in examples/tailwind/ and load a page in a browser. The console should show a warning about nested CSS.

  [WARN] [vite] [vite:css] Nested CSS was detected, but CSS nesting has not been configured correctly.
  Please enable a CSS nesting plugin *before* Tailwind in your configuration.
  See how here: https://tailwindcss.com/docs/using-with-preprocessors#nesting
  29 |  		max-width: 100%;
  30 |
  31 |  		&::marker,
    |    ^^^^^^^^^^
  32 |  		&::-webkit-details-marker {
    |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  33 |  			color: var(--sl-color-gray-3);
    |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  34 |  		}
    |  ^^^
  

• With the changes, running the same scenario does not show the warning.

[changeset-bot]

🦋 Changeset detected

Latest commit: 00c6790

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/starlight	Patch

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Name	Status	Preview	Updated (UTC)
starlight	✅ Ready (Inspect)	Visit Preview	Mar 19, 2024 9:04pm

[delucis]

Thanks for cleaning this up @HiDeoo! One day, we will all live in CSS nesting paradise, but for now, this will have to do 😁