Hide default slider background

[hannahblair]

Description

Fixes the slider background showing in Firefox in dark mode.

Closes: #9641

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[gradio-pr-bot]

🪼 branch checks and previews

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---

Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/cce9d038425bc26fc70c860a51831f26c7c67a87/gradio-5.1.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@cce9d038425bc26fc70c860a51831f26c7c67a87#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/cce9d038425bc26fc70c860a51831f26c7c67a87/gradio-client-1.6.0.tgz

Use Lite from this PR

<script type="module" src="https://gradio-lite-previews.s3.amazonaws.com/cce9d038425bc26fc70c860a51831f26c7c67a87/dist/lite.js""></script>

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/slider	patch
gradio	patch

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With the following changelog entry.

Hide default slider background

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[abidlabs]

Tested, confirms this fixes the issue on firefox! For some reason, dark mode isn't working for me on Chrome, but assuming it still looks good in dark mode, should be good to merge

[blaisewf]

Also works fine here!