Does this issue occur when all extensions are disabled?: Yes/No
Yes

• VS Code Version: Version: 1.88.0-insider (Universal), Commit: b403212, Date: 2024-03-21T17:26:53.619Z (9 hrs ago)
• OS Version: OS: Darwin arm64 23.2.0

Steps to Reproduce:

1. Run code-insiders serve-web --server-base-path /foo/bar --port 8884 --host 0.0.0.0 --without-connection-token --log debug
2. Open the code server URL in the browser
3. Notice that the Activity Bar icons are not visible, it looks like the theme is broken.
4. if the serve-web is launched without server-base-path option at a given port, for example 8884, and then after accessing it from the browser, if the server is started with --server-base-path /foo/bar, then the issue is masked, perhaps because of browser caching.