text: Title: [docs] "Adding custom CSS to your demo" is not updated for 5.0
  Body: ### Describe the bug
  
   "For additional styling ability, you can pass any CSS to your app using the css= kwarg. You can either the filepath to a CSS file, or a string of CSS code." silently fails for css from a file path since 5.0. 
  
  This is mentioned in #9463 but not updated in the doc.
  
  See also #10344 for another issue on that page.
  
  ### Have you searched existing issues?  🔎
  
  - [x] I have searched and found no existing issues
  
  ### Reproduction
  
  Prerequisites: `styles.css` in the same directory defining `some-style`
  
  ```python
  import gradio as gr
  
  with gr.Blocks(fill_height=True, css="styles.css") as demo:
      gr.Textbox(label="Time", elem_classes="some-style")
  
  ```
  
  fails silently.
  
  The correct parameter for css from a file path:
  
  ```
  css_paths="styles.css"
  ```
  
  ### Screenshot
  
  _No response_
  
  ### Logs
  
  ```shell
  
  ```
  
  ### System Info
  
  ```shell
  Gradio >= 5.0
  ```
  
  ### Severity
  
  I can work around it