Can't add tailwindcss to an existing Shopify store (Theme Dawn)

[GUIGUI69PRO]

Firstly, I clone Dawn Theme locally :

shopify theme init --clone-url https://github.com/Shopify/dawn.git

Then I begin the installation :
npm install -D tailwindcss
npx tailwindcss init

The file tailwind.config.js appear. I complete like that :

/** @type {import('tailwindcss').Config} /
module.exports = {
content: [
'./config/.json',
'./layout/.liquid',
'./assets/.liquid',
'./sections/.liquid',
'./snippets/.liquid',
'./templates/.liquid',
'./templates/.json',
'./templates/customers/*.liquid',
],
theme: {
extend: {},
},
plugins: [],
}

Then, next step.

I create a file in assets named app-tailwind.css in wich in put this :

@tailwind base;
@tailwind components;
@tailwind utilities;

Then

npx tailwindcss -i ./assets/app-tailwind.css -o ./assets/app.css --watch

A new file app.css appear in assets.

Then I put my css into my theme.liquid

{{ 'app.css' | asset_url | stylesheet_tag }}
{{ 'base.css' | asset_url | stylesheet_tag }}

AND THEN when I create a new section section-test.liquid TailwindCss doesn't work ...

After a shopify theme serve and customize the website with putting the section online, this is what appear

Or, sometimes, it appears like that, smaller than wanted :

Thanks so much