[BUG] Preview panel content renders on left side overlapping chat instead of in the right-side panel area

Preflight

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

When using the Preview panel in the Claude Code Desktop app (Windows), the preview content (browser view) renders on the left side overlapping the chat conversation instead of staying inside the right-side panel area where the gray background is.

The gray background placeholder for the Preview panel appears correctly on the right side, but the actual rendered content (the browser view showing the dev server) overlays on top of the chat text on the left, making the conversation unreadable.

Workaround: Clicking the three-dot menu (⋮) next to the Preview tab temporarily fixes the layout — the preview snaps into its correct position on the right. However, as soon as the menu is dismissed (clicking elsewhere), the preview content jumps back to the left side, overlapping the chat again.

What Should Happen?

The Preview panel content should render inside the right-side panel area (where the gray background is), without overlapping the chat conversation on the left.

Steps to Reproduce

1. Open Claude Code Desktop app on Windows 11
2. Start a dev server using Preview (e.g., configure .claude/launch.json and run preview_start)
3. The Preview panel opens — notice the gray background area is on the right, but the actual browser content renders on the left, overlapping the chat
4. Click the three-dot menu (⋮) next to the Preview tab — the layout corrects itself temporarily
5. Click anywhere else to dismiss the menu — the preview jumps back to the left side

Claude Model

Opus 4.6

Is this a regression?

I don't know

Claude Code Version

Latest (always kept up to date)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

• Terminal: Claude Code Desktop App (Windows native app, not CLI in a terminal)
• OS: Windows 11 Home 10.0.26200
• Plan: Max plan

This appears to be a CSS/layout issue specific to the Preview panel positioning in the Desktop app on Windows.