[BUG] Invisible scroll list

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Title: Scrollbar thumb becomes nearly invisible near the bottom of the chat panel (VS Code extension)

Environment:

• OS: Windows 11
• Editor: VS Code
• Claude Code extension (VS Code integration)

Description:
The scrollbar thumb in the Claude Code chat panel is clearly visible (a solid, appropriately-sized bar) when scrolled to the middle/top of the conversation. When scrolled near the bottom of the panel, the same thumb shrinks to a tiny, barely-visible sliver — a size change, not just a color/contrast issue.

Steps to reproduce:

1. Open the Claude Code panel in VS Code with a long conversation (enough content to scroll).
2. Scroll to the middle of the conversation — note the scrollbar thumb's size/visibility.
3. Scroll to the very bottom of the panel.
4. Compare — the thumb becomes much smaller/fainter near the bottom.

Expected: the scrollbar thumb should stay a consistent, visible size regardless of scroll position (matching standard VS Code scrollbar behavior).

Actual: thumb shrinks dramatically near the bottom, making it very hard to see or grab.

Additional notes:

• Tried customizing workbench.colorCustomizations (scrollbarSlider.background/hoverBackground/activeBackground, scrollbar.shadow) in user settings.json — no effect on this specific panel, suggesting the chat panel renders its own scrollbar (e.g. inside a webview) independent of the standard VS Code theme tokens.
• Screenshots attached showing the size difference between mid-scroll and bottom-of-scroll positions.

What Should Happen?

Should be visible all the way up and down

Error Messages/Logs

Steps to Reproduce

Scroll from top to bottom

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.278 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

<img width="342" height="372" alt="Image" src="https://github.com/user-attachments/assets/5c898cde-d545-45ec-9933-3fcc1dfda6fc" />

<img width="437" height="366" alt="Image" src="https://github.com/user-attachments/assets/cf8ecdd4-cae6-4ce5-8ffd-90280379c20d" />