Allow applying @media, @keyframes and @import in custom CSS

[hannahblair]

Description

Our custom CSS logic was only applying CSS rules with the type CSSStyleRule, which meant that other rule types including CSSMediaRule and CSSKeyframesRule weren't being applied. This fixes that, and adds a demo and an e2e test to ensure all three rules are applied.

Closes: #7390

🎯 PRs Should Target Issues

Before your create a PR, please check to see if there is an existing issue for this change. If not, please create an issue before you create this PR, unless the fix is very small.

Not adhering to this guideline will result in the PR being closed.

Tests

1. PRs will only be merged if tests pass on CI. To run the tests locally, please set up your Gradio environment locally and run the tests: bash scripts/run_all_tests.sh

2. You may need to run the linters: bash scripts/format_backend.sh and bash scripts/format_frontend.sh

[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
	Website	ready!	Website preview
	Storybook	ready!	Storybook preview
🦄	Changes	detected!	Details

---

Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/e41ad4edde5cff58f561cf092e23778ab7a67035/gradio-4.18.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@e41ad4edde5cff58f561cf092e23778ab7a67035#subdirectory=client/python"

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/app	patch
gradio	patch

• Maintainers can select this checkbox to manually select packages to update.

With the following changelog entry.

Allow applying @media, @keyframes and @import in custom CSS

Maintainers or the PR author can modify the PR title to modify this entry.

Something isn't right?

• Maintainers can change the version label to modify the version bump.
• If the bot has failed to detect any changes, or if this pull request needs to update multiple packages to different versions or requires a more comprehensive changelog entry, maintainers can update the changelog file directly.

[dawoodkhan82]

Otherwise lgtm!