Why Isn\'t My Flask App Loading My CSS File?

Application Not Picking Up .css File: A Guide to Modifying Flask File Structure

When styling external style sheets in a Flask application, it is necessary to structure the files appropriately to ensure the styles are applied successfully. If the styles are not being applied, the file structure may need to be adjusted.

In the given example, the external style sheet is located at /styles/mainpage.css, while the HTML template tries to load it from ../styles/mainpage.css. This incorrect path is likely causing the styles to not apply.

To fix this issue, the file structure should be modified to place the style sheet within the application's "static" folder. The updated file structure should look like this:

/app
    - app_runner.py
    /services
        - app.py 
    /templates
        - mainpage.html
    /static
        /styles
            - mainpage.css

Next, the HTML template should be adjusted to load the CSS file correctly:

<link rel="stylesheet" type="text/css" href="%7B%7B%20url_for('static',%20filename='styles/mainpage.css')%20%7D%7D">

This modified HTML code uses the url_for function to dynamically generate the correct URL for the CSS file, ensuring Flask can find it within the "static" folder. Upon implementing these changes, the external styles should now be applied to the rendered template.

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