fix(compiler): use posix separators for nested stylesheet imports

[anxkhn]

All Submissions

• Have you followed the guidelines stated in CONTRIBUTING.md?
• Have you checked to ensure there aren't any other open Pull Requests for the desired change?

Type of change

• Bug fix (non-breaking change which fixes an issue)

Changes To Core Features

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully run tests with your changes locally?

What and why

Nested/subfolder stylesheets silently fail to load on Windows.

_compile_root_stylesheet (reflex/compiler/compiler.py) builds the relative
target as a pathlib.Path and then emits it into a CSS @import:

target_path = stylesheet.relative_to(assets_app_path).with_suffix(".css")
...
str_target_path = "./" + str(target_path)   # OS-dependent separator

For a nested stylesheet, str(Path("subdir/theme.css")) is
"subdir\\theme.css" on Windows, so the compiler writes:

@import url('./subdir\theme.css');

Per the CSS spec, a backslash inside url() is an escape-sequence introducer,
not a path separator (\t becomes a hex escape), so the browser requests a
mangled URL and the stylesheet never loads. This only happens on Windows;
POSIX already renders /, which is why it went unnoticed. Nested stylesheets
are explicitly supported: rx.App(stylesheets=["subdir/theme.css"]), and a
directory stylesheet is expanded via rglob into arbitrarily deep files, both
of which yield multi-segment relative paths.

The fix normalizes the import URL to forward slashes on every platform:

str_target_path = "./" + target_path.as_posix()

On POSIX the output is byte-for-byte identical to before, so only Windows
behavior changes. This mirrors the separator-normalization idiom already used
elsewhere in the compiler (e.g. reflex/compiler/utils.py).

Tests

• Added test_compile_stylesheets_nested_import_uses_posix_separators in
  tests/units/compiler/test_compiler.py. It simulates Windows by forcing the
  relative path to a PureWindowsPath and asserts the emitted import is
  @import url('./subdir/theme.css'); with no backslash. It fails before the
  fix (emitting @import url('./subdir\theme.css');) and passes after.
• Made two existing scss/sass assertions in the same file separator-independent
  so they express the intended forward-slash output directly.
• uv run pytest tests/units/compiler -q -> 180 passed.
• uv run ruff check . / uv run ruff format --check -> clean.
• uv run pyright reflex tests -> 0 errors.

---

## Commits on the branch (2)

f7ec2402 fix(compiler): use posix separators for nested stylesheet imports
4f3b39fd fix(compiler): add changelog fragment for nested stylesheet posix fix

Both are GitHub-verified (ED25519, signature `G`) and carry a `Signed-off-by`
trailer. Diff: 3 files, +60/-6.

- `reflex/compiler/compiler.py` - one-line fix (`str(...)` -> `.as_posix()`) plus a
  three-line inline comment explaining the CSS-escape hazard.
- `tests/units/compiler/test_compiler.py` - new regression test + two assertions
  made separator-independent.
- `news/6725.bugfix.md` - towncrier changelog fragment (one user-facing sentence).

[greptile-apps]

Greptile Summary

This PR fixes nested stylesheet imports on Windows. The main changes are:

• Emits CSS import paths with POSIX separators.
• Adds a Windows-path test for nested stylesheets.
• Updates Sass and SCSS expectations to use forward slashes.
• Adds a bug-fix changelog entry.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
reflex/compiler/compiler.py	Uses Path.as_posix() when rendering local stylesheet paths into CSS import URLs.
tests/units/compiler/test_compiler.py	Adds coverage for Windows-style nested paths and makes related expected URLs platform-independent.
news/6725.bugfix.md	Documents the Windows nested-stylesheet import fix.

_{Reviews (1): Last reviewed commit: "fix(compiler): add changelog fragment fo..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing anxkhn:patch-9 (366ade7) with main (32cc257)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩