When I host a Flask application in Docker on my PC, the CSS and JS are read correctly from a template and HTML view formatted. When I host the same application in Kubernetes POD, it does not read CSS and JS.

In a snapshot below you can see a result. Below please find a file structure of the app. Views index.html and upload.html are extending public/templates/public_template.html which consists of imports of CSS and JS libraries.

Could you please tell what could be the reason? Could the required file structure be different between kubectl and Docker?

C:.
|   .gitignore
|   Dockerfile
|   upload_app-deploy.yaml
|   run.py
|
\---app
    |   app.py
    |   requirements.txt
    |   __init__.py
    |
    +---static
    |   +---css
    |   |       bootstrap.min.css
    |   |       style.css
    |   |
    |   +---img
    |   |       flask.png
    |   |
    |   \---js
    |           app.js
    |           bootstrap.bundle.min.js
    |           jquery.slim.min.js
    |
    \---templates
        +---admin
        |   \---templates
        \---public
            |   index.html
            |   upload.html
            |
            \---templates
                    public_template.html 

Error in the browser:

Failed to load resource: the server responded with a status of 403 ()
jquery.slim.min.js:1 Failed to load resource: the server responded with a status of 403 ()
(index):1 Refused to apply style from 'https://ais-bt-services.asml.com/static/css/style.css' because its MIME type ('text/html') is not a supported stylesheet MIME type, and strict MIME checking is enabled.
app.js:1 Failed to load resource: the server responded with a status of 403 ()
(index):1 Refused to apply style from 'https://ais-bt-services.asml.com/static/css/bootstrap.min.css' because its MIME type ('text/html') is not a supported stylesheet MIME type, and strict MIME checking is enabled.

Dockerfile:

# Python 3 running on Debian GNU/Linux 10 (buster)(ATM) (amd64)
FROM XXX/docker/python:3

# Fill directories
COPY . /app

# Switch default directory so f.e. you don't have to provide a full pwd of req.txt
WORKDIR /app/app

# Install python packages with fixed versions
RUN pip install --force-reinstall -r requirements.txt

# Execute an app: listener and handler
CMD ["python", "/app/app/app.py"]

Below please find permissions to the catalogues, they seem OK to me, directories to 775 and files to 664 and the root user. Could it be that a user is different once running in Kubernetes? Or maybe any other ideas?