Bump @adobe/css-tools from 4.0.1 to 4.3.1 in /demo/client

Bumps [@adobe/css-tools](https://github.com/adobe/css-tools) from 4.0.1 to 4.3.1.
- [Changelog](https://github.com/adobe/css-tools/blob/main/History.md)
- [Commits](https://github.com/adobe/css-tools/commits)

---
updated-dependencies:
- dependency-name: "@adobe/css-tools"
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>