Grouped Accordion Border Color

### Describe the bug Grouped accordions are being given a thick, high contrast border when grouped. This can't be reproduced on main, because the border width has recently been set to 0, but the border color is still wrong, so this is likely to regress. It was introduced between `6.7.0` and `6.8.0` and persists up to `6.16.0`. ### Have you searched existing issues? 🔎 - [x] I have searched and found no existing issues ### Reproduction ```python import gradio as gr with gr.Blocks() as demo: with gr.Group(): with gr.Accordion("Test"): gr.Button() gr.Button() with gr.Accordion("Test"): gr.Button() gr.Button() demo.launch() ``` ### Screenshot <img width="603" height="289" alt="Image" src="https://github.com/user-attachments/assets/e8d61626-4d18-40e6-9f60-5ac3f7dd7df3" /> <img width="490" height="291" alt="Image" src="https://github.com/user-attachments/assets/6cde1e6c-9eb3-493f-9415-942ac4593c19" /> ### Logs ```shell ``` ### System Info ```shell gradio 6.16.0 ``` ### Severity I can work around it