TailwindCSS: Issue with Project Root Directory when Configuring tailwindcss.config.js - tailwind-css

Question

Tailwindcss documentation states that files in the content
section of tailwind.config.js are resolved relative to the
"project root" directory.
My question is, what does "project root" directory refers to?
the directory containing tailwindcss.config.js?
the directory containing package.json? (a project can have multiple of those)
the root git directory( directory containing.git )?
the current working directory of the tailwindcss command?
That is, the directory where the command is invoked in.
the directory containing the actual binary of tailwindcss CLI?
Update
Okay, if I am not mistaken the working directory of tailwindcss is treated as the project root directory.
For example, if your project layout is something like this:
./my-project
|_ src
| |_ index.html
|_ tailwind.config.js
And, tailwindcss is invoked from the root of your project like this:
cd ./myproject
tailwindcss --config tailwind.config.js [other options]
Then, your tailwind.config.js should be configured as:
module.exports = {
content: ["./src/index.html"],
};
However, if we switch into the src directory and call tailwindcss:
cd ./myproject/src
tailwindcss --config tailwind.config.js [other options]
Then, tailwind.config.js should read something like this:
module.exports = {
content: ["./index.html"],
};