rustdoc: `--extend-css` option refers to ../static.files/theme.css but puts css in ../theme.css

[monkeydom]

When adding an --extend-css file, it seems that the file gets copied to the wrong location or that it is referenced incorrectly.

Steps:

> cargo new --lib ecss
     Created library `ecss` package
> cd ecss
> cat >custom.css <<<"body {background: red;}"
> RUSTDOCFLAGS="--extend-css $PWD/custom.css" cargo doc --open

Expected Results:

Red background in docs

Actual Results:

No red background

Notes:

Moving the theme.css to static.files/theme.css fixes the issue

> cp target/doc/theme.css target/doc/static.files/

Just for reference, this is the cmd line cargo generates:

rustdoc --edition=2021 --crate-type lib --crate-name ecss src/lib.rs -o /Users/dom/Data/Playground/rust/ecss/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=115 -C metadata=b5a7f46f1030585c -L dependency=/Users/dom/Data/Playground/rust/ecss/target/debug/deps --extend-css /Users/dom/Data/Playground/rust/ecss/custom.css --crate-version 0.1.0

and the header line in the index.html

<link rel="stylesheet" href="../static.files/theme.css">

Context & Version

> rustdoc --version
rustdoc 1.68.2 (9eb3afe9e 2023-03-27)

> sw_vers
ProductName:		macOS
ProductVersion:		13.3
BuildVersion:		22E252