Why Isn\'t My Flask Application Recognizing My External CSS File?

CSS File Not Recognized in Flask Application: Troubleshooting File Structure

When attempting to style a template using an external CSS file in Flask, it's essential to ensure your file structure is correct. If your styles aren't applying, consider the following:

File Structure:

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

HTML Markup:

  
    <link rel="stylesheet" type="text/css" href="../styles/mainpage.css">
  
  
    <!-- content -->
  

Issue:

Your CSS file is located outside the "static" folder, which Flask uses to serve static files such as CSS and JavaScript.

Solution:

To resolve this, move your CSS file under the "static" folder, and update your HTML file accordingly:

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

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

Explanation:

Flask looks for static files under the "static" folder, allowing you to serve CSS files without managing their file paths explicitly. By using this approach, your application will now correctly apply the styles defined in your external "mainpage.css" file.

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