feat: CSS language plugin

.gitattributes

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+# Convert text file line endings to lf
+* text=auto
+
+*.js text eol=lf

.github/ISSUE_TEMPLATE/bug-report.yml

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+name: "\U0001F41E Report a problem"
+description: "Report something that isn't working the way you expected."
+title: "Bug: (fill in)"
+labels:
+    - bug
+    - "repro:needed"
+body:
+    - type: markdown
+      attributes:
+          value: By opening an issue, you agree to abide by the [OpenJS Foundation Code of Conduct](https://eslint.org/conduct).
+    - type: textarea
+      attributes:
+          label: Environment
+          description: |
+              Please tell us about how you're running ESLint (Run `npx eslint --env-info`.)
+          value: |
+              ESLint version: 
+              @eslint/css version: 
+              Node version: 
+              npm version: 
+              Operating System:
+      validations:
+          required: true
+    - type: dropdown
+      attributes:
+          label: Which language are you using?
+          description: |
+              Just tell us which language mode you're using.
+          options:
+              - stylesheet
+              - rule
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What did you do?
+          description: |
+              Please include a *minimal* reproduction case.
+          value: |
+              <details>
+              <summary>Configuration</summary>
+
+              ```
+              <!-- Paste your configuration here -->
+              ```
+              </details>
+
+              ```js
+              <!-- Paste your code here -->
+              ```
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What did you expect to happen?
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What actually happened?
+          description: |
+              Please copy-paste the actual ESLint output.
+      validations:
+          required: true
+    - type: input
+      attributes:
+          label: Link to Minimal Reproducible Example
+          description: "Link to a [StackBlitz](https://stackblitz.com), or GitHub repo with a minimal reproduction of the problem. **A minimal reproduction is required** so that others can help debug your issue. If a report is vague (e.g. just a generic error message) and has no reproduction, it may be auto-closed."
+          placeholder: "https://stackblitz.com/abcd1234"
+      validations:
+          required: true
+    - type: checkboxes
+      attributes:
+          label: Participation
+          options:
+              - label: I am willing to submit a pull request for this issue.
+                required: false
+    - type: textarea
+      attributes:
+          label: Additional comments
+          description: Is there anything else that's important for the team to know?

.github/ISSUE_TEMPLATE/change.yml

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+name: "\U0001F680 Request a change (not rule-related)"
+description: "Request a change that is not a bug fix, rule change, or new rule"
+title: "Change Request: (fill in)"
+labels:
+    - enhancement
+    - core
+body:
+    - type: markdown
+      attributes:
+          value: By opening an issue, you agree to abide by the [OpenJS Foundation Code of Conduct](https://eslint.org/conduct).
+    - type: textarea
+      attributes:
+          label: Environment
+          description: |
+              Please tell us about how you're running ESLint (Run `npx eslint --env-info`.)
+          value: |
+              ESLint version: 
+              @eslint/css version: 
+              Node version: 
+              npm version: 
+              Operating System:
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What problem do you want to solve?
+          description: |
+              Please explain your use case in as much detail as possible.
+          placeholder: |
+              The CSS plugin currently...
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What do you think is the correct solution?
+          description: |
+              Please explain how you'd like to change the CSS plugin to address the problem.
+          placeholder: |
+              I'd like the CSS plugin to...
+      validations:
+          required: true
+    - type: checkboxes
+      attributes:
+          label: Participation
+          options:
+              - label: I am willing to submit a pull request for this change.
+                required: false
+    - type: textarea
+      attributes:
+          label: Additional comments
+          description: Is there anything else that's important for the team to know?

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false
+contact_links:
+    - name: 🗣 Ask a Question, Discuss
+      url: https://github.com/eslint/css/discussions
+      about: Get help using this plugin
+    - name: Discord Server
+      url: https://eslint.org/chat
+      about: Talk with the team

.github/ISSUE_TEMPLATE/docs.yml

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+name: "\U0001F4DD Docs"
+description: "Request an improvement to documentation"
+title: "Docs: (fill in)"
+labels:
+    - documentation
+body:
+    - type: markdown
+      attributes:
+          value: By opening an issue, you agree to abide by the [OpenJS Foundation Code of Conduct](https://eslint.org/conduct).
+    - type: textarea
+      attributes:
+          label: Docs page(s)
+          description: |
+              What page(s) are you suggesting be changed or created?
+          placeholder: |
+              e.g. https://eslint.org/docs/latest/use/getting-started
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What documentation issue do you want to solve?
+          description: |
+              Please explain your issue in as much detail as possible.
+          placeholder: |
+              The docs currently...
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What do you think is the correct solution?
+          description: |
+              Please explain how you'd like to change the docs to address the problem.
+          placeholder: |
+              I'd like the docs to...
+      validations:
+          required: true
+    - type: checkboxes
+      attributes:
+          label: Participation
+          options:
+              - label: I am willing to submit a pull request for this change.
+                required: false
+    - type: textarea
+      attributes:
+          label: Additional comments
+          description: Is there anything else that's important for the team to know?

.github/ISSUE_TEMPLATE/new-rule.yml

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+name: "\U0001F680 Propose a new rule"
+description: "Propose a new rule to be added to the plugin"
+title: "New Rule: (fill in)"
+labels:
+    - rule
+    - feature
+body:
+    - type: markdown
+      attributes:
+          value: By opening an issue, you agree to abide by the [OpenJS Foundation Code of Conduct](https://eslint.org/conduct).
+    - type: input
+      attributes:
+          label: Rule details
+          description: What should the new rule do?
+      validations:
+          required: true
+    - type: dropdown
+      attributes:
+          label: What type of rule is this?
+          options:
+              - Warns about a potential problem
+              - Suggests an alternate way of doing something
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: Example code
+          description: Please provide some example code that this rule will warn about. This field will render as CSS.
+          render: css
+      validations:
+          required: true
+    - type: checkboxes
+      attributes:
+          label: Participation
+          options:
+              - label: I am willing to submit a pull request to implement this rule.
+                required: false
+    - type: textarea
+      attributes:
+          label: Additional comments
+          description: Is there anything else that's important for the team to know?

.github/ISSUE_TEMPLATE/rule-change.yml

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+name: "\U0001F4DD Request a rule change"
+description: "Request a change to an existing rule"
+title: "Rule Change: (fill in)"
+labels:
+    - enhancement
+    - rule
+body:
+    - type: markdown
+      attributes:
+          value: By opening an issue, you agree to abide by the [OpenJS Foundation Code of Conduct](https://eslint.org/conduct).
+    - type: input
+      attributes:
+          label: What rule do you want to change?
+      validations:
+          required: true
+    - type: dropdown
+      attributes:
+          label: What change do you want to make?
+          options:
+              - Generate more warnings
+              - Generate fewer warnings
+              - Implement autofix
+              - Implement suggestions
+      validations:
+          required: true
+    - type: dropdown
+      attributes:
+          label: How do you think the change should be implemented?
+          options:
+              - A new option
+              - A new default behavior
+              - Other
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: Example code
+          description: Please provide some example code that this change will affect. This field will render as CSS.
+          render: css
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What does the rule currently do for this code?
+      validations:
+          required: true
+    - type: textarea
+      attributes:
+          label: What will the rule do after it's changed?
+      validations:
+          required: true
+    - type: checkboxes
+      attributes:
+          label: Participation
+          options:
+              - label: I am willing to submit a pull request to implement this change.
+                required: false
+    - type: textarea
+      attributes:
+          label: Additional comments
+          description: Is there anything else that's important for the team to know?

.github/PULL_REQUEST_TEMPLATE.md

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+<!--
+    Thank you for contributing!
+
+    ESLint adheres to the [OpenJS Foundation Code of Conduct](https://eslint.org/conduct).
+-->
+
+#### Prerequisites checklist
+
+-   [ ] I have read the [contributing guidelines](https://github.com/eslint/eslint/blob/HEAD/CONTRIBUTING.md).
+
+<!--
+    Please ensure your pull request is ready:
+
+    - Read the pull request guide (https://eslint.org/docs/latest/contribute/pull-requests)
+    - Update or create tests
+    - If performance-related, include a benchmark
+    - Update documentation for this change (if appropriate)
+-->
+
+<!--
+    The following is required for all pull requests:
+-->
+
+#### What is the purpose of this pull request?
+
+#### What changes did you make? (Give an overview)
+
+#### Related Issues
+
+<!-- include tags like "fixes #123" or "refs #123" -->
+
+#### Is there anything you'd like reviewers to focus on?
+
+<!-- markdownlint-disable-file MD004 -->

.github/workflows/bun-test.yml

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+name: Bun CI
+
+on:
+    push:
+        branches:
+            - main
+    pull_request:
+        branches:
+            - main
+
+jobs:
+    build:
+        runs-on: ${{ matrix.os }}
+
+        strategy:
+            matrix:
+                os: [windows-latest, macOS-latest, ubuntu-latest]
+                bun: [latest]
+
+        steps:
+            - uses: actions/checkout@v4
+            - name: Use Bun ${{ matrix.bun }} ${{ matrix.os }}
+              uses: oven-sh/setup-bun@v1
+              with:
+                  bun-version: ${{ matrix.bun }}
+            - name: bun install, build, and test
+              run: |
+                  bun install
+                  bun run --bun test
+              env:
+                  CI: true