Window tab unreadable

When setting `"use_system_window_tabs": true`, and combine multiple windows, the tab part is too transparent and if the background is too bright, the text is unreadable. Also it doesn't look good anymore aesthetically.

<img width="1754" height="925" alt="Image" src="https://github.com/user-attachments/assets/d98cdae4-1c0a-4dec-84ee-cfecf4626773" />