add tailwind to rust build script

build.rs

use std::process::Command;

fn main() {
	let tailwind_cmd = "npx tailwindcss -i input.css -o assets/app.css";

	if cfg!(target_os = "windows") {
		Command::new("cmd").arg("/C").arg(tailwind_cmd).status()
	} else {
		Command::new("sh").arg("-c").arg(tailwind_cmd).status()
	}
	.expect("error running tailwind");

	println!("cargo:rerun-if-changed=tailwind.config.js");
	println!("cargo:rerun-if-changed=input.css");
}

You have the check status.success(), because .status() only returns Err in certain cases (there was something wrong at the system level that disallowed running the command.) Here is my version...

use std::{
    io::{self, Write},
    process,
};

fn main() {
    println!("cargo:rerun-if-changed=tailwind.config.js");
    println!("cargo:rerun-if-changed=src/input.css");

    match process::Command::new("sh")
        .arg("-c")
        .arg("npx tailwindcss -i src/input.css -o target/output.css")
        .output()
    {
        Ok(output) => {
            if !output.status.success() {
                let _ = io::stdout().write_all(&output.stdout);
                let _ = io::stdout().write_all(&output.stderr);
                panic!("Tailwind error");
            }
        }
        Err(e) => panic!("Tailwind error: {:?}", e),
    };
}

Which produces error messages like this...

$ cargo run --release
   Compiling twind1 v0.1.0 (/Users/bedwards/code/twind1)
error: failed to run custom build command for `twind1 v0.1.0 (/Users/bedwards/code/twind1)`

Caused by:
  process didn't exit successfully: `/Users/bedwards/code/twind1/target/release/build/twind1-7b30e541e618a4b0/build-script-build` (exit status: 101)
  --- stdout
  cargo:rerun-if-changed=tailwind.config.js
  cargo:rerun-if-changed=src/input.css
  Specified input file src/input.css does not exist.

  --- stderr
  thread 'main' panicked at build.rs:19:17:
  Tailwind error

excellent!