[BUG] Claude in Chrome: High CPU usage (~50% on M1) from border glow box-shadow animation

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?

The .claude-agent-glow-border overlay uses a CSS box-shadow animation (claude-pulse) that's CPU-heavy. Box-shadow isn't GPU-accelerated, and with multiple layered inset shadows animating infinitely, it causes unnecessary paint operations every frame. Google Chrome Helper immediately jumps to ~50% CPU on Apple M1 while the agent is using an active tab.

<img width="1725" height="996" alt="Image" src="https://github.com/user-attachments/assets/0f73d170-a023-43e9-a64e-c64fffed306d" />

What Should Happen?

Use GPU-accelerated properties instead: animate opacity or transform on a pseudo-element with a static border/gradient, or use border-image. These composite on the GPU without triggering repaints.

Error Messages/Logs

Steps to Reproduce

Open Claude in Chrome.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.15

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

_No response_