[Feature Request] Add options to hide the sidebar, use an all-white background, and extend the width of the content area further.

### 🥰 Feature Description

For my setup, I use a vertical monitor, and the sidebar is too large, which makes the content area shorter. Could you add an option to hide the sidebar? Also, for the chat theme, could we have an all-white background, or a white/clear background? This would make it easier to read, just like on the ChatGPT or Gemini web interfaces. And also, add an option to extend the width of the content area further.

### 🧐 Proposed Solution


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### 📝 Additional Information

It's easy to have a wider content area on both vertical and horizontal monitors, along with a white background and the option to hide the sidebar, just like on the ChatGPT or Gemini web interfaces. It looks more modern.