Fix chat input border colors and animation duration

[mrleemurray]

This pull request updates the animated border colors for the chat input component to better align with the button background color, ensuring a more consistent and visually appealing theme across both light and dark modes. Additionally, it speeds up the chat send button's spinning animation for a snappier user experience.

Theme and color improvements:

• Updated the definitions of chat.inputWorkingBorderColor1, chat.inputWorkingBorderColor2, and chat.inputWorkingBorderColor3 in chatColors.ts to derive their values from the buttonBackground color, using darken and lighten utilities for secondary and tertiary colors. This ensures the chat input border colors are consistent with button styling across themes.
• Changed the values of chat.inputWorkingBorderColor1, chat.inputWorkingBorderColor2, and chat.inputWorkingBorderColor3 in both 2026-dark.json and 2026-light.json to match the new color scheme, further aligning theme files with the updated color logic. [1] [2]
• Added imports for buttonBackground, darken, and lighten in chatColors.ts to support the new color calculations.

UI/Animation tweaks:

• Reduced the duration of the chat-send-button-spin animation from 18 seconds to 8 seconds in chatInput.css, making the send button's activity indicator more responsive and noticeable. [1] [2]

[Copilot]

Pull request overview

Adjusts chat input “working” border color tokens to better align with button theming and speeds up the Sessions send-button gradient rotation to improve perceived responsiveness.

Changes:

• Updated chat.inputWorkingBorderColor{1,2,3} defaults to derive from button.background (with lighten/darken transforms).
• Reduced the experimental Sessions send-button gradient rotation animation duration from 18s to 8s.
• Updated 2026 light/dark default theme overrides for the three chat input working border colors.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/vs/workbench/contrib/chat/common/widget/chatColors.ts	Derives chat input working border color tokens from button.background (and transforms) for improved visibility/consistency.
src/vs/sessions/contrib/chat/browser/media/chatInput.css	Speeds up the gradient rotation animation for the Sessions send button.
extensions/theme-defaults/themes/2026-light.json	Updates 2026 light theme values for chat input working border colors.
extensions/theme-defaults/themes/2026-dark.json	Updates 2026 dark theme values for chat input working border colors.