reload on css changes + fix css specificity

[pngwn]

Description

This has been driving me up the wall all weekend, so here is a fix.

• Ensure the app reloads + css is correctly applied when CSS files in a watch dir are edited. cc @freddyaboulton
• Ensure CSS is correctly applied when CSS (as a string) changed.
• Make working with custom CSS much simpler (genuine fix for setting css not effective #3851) cc @aliabid94 @abidlabs

This should work fine now with no need for !important modifiers or other CSS hacks:

import gradio as gr

css = """
#custom-md h1 {
  color: hotpink;
}

.custom-md h2 {
  color: orange;
}
"""

with gr.Blocks(css=css) as demo:
  gr.Markdown("# Heading one", elem_id="custom-md")
  gr.Markdown("## Heading two", elem_classes=["custom-md"])

demo.launch()

We do this by modifying the selectors passed by a user, prepending them with a series of addition selectors to increase their specificity enough that they override the svelte hashed classes. It's hacky but should be relatively robust.

Closes #6735. Closes #6736.

[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
	Website	ready!	Website preview
	Storybook	ready!	Storybook preview
	Visual tests	all good!	Build review
🦄	Changes	detected!	Details

---

Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/cfe5f674856711cd15408b80616774720313e920/gradio-4.8.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@cfe5f674856711cd15408b80616774720313e920#subdirectory=client/python"

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/app	minor
@gradio/preview	minor
gradio	minor

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With the following changelog entry.

reload on css changes + fix css specificity

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• 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.

[pngwn]

gradio cc dev was completely broken on main because of a dependency issue, I've fixed that in this branch too.

[pngwn]

Need to merge to check some other issues. Feel free to review and I'll address anything in another PR

[abidlabs]

Nice. I don't think repeating a css rule should have any (non-performance-related) downsides so this should be good

[pngwn]

The number of rules should generally be pretty modest, so I think the performance should be ok.

[abidlabs]

Cool, looks great to me @pngwn! Thanks for dogfooding this workflow :)