Agents: Refactor chat experimental send button styles

[mrleemurray]

This pull request updates the styling of the experimental chat send button gradient to create a calmer, more consistent appearance and interaction experience. The changes simplify the hover/focus effect, adjust animation transitions, and clarify documentation comments to better describe the visual intent.

Styling and interaction improvements:

• The send button at rest now uses a slowly rotating, darkened conic gradient fill instead of a gradient ring, providing a calmer and more modern look. [1] [2] [3]
• On hover and focus, the button now displays a subtle dark overlay using an inset box-shadow, matching standard toolbar button feedback and preserving the gradient underneath, instead of a multi-color glow. [1] [2]
• The transition duration for the box-shadow effect is reduced from 250ms to 120ms for a snappier response. [1] [2]

Documentation and comment updates:

• CSS comments are updated to clarify that colors are darkened for a calm fill, and to better explain the visual rationale behind the gradient and overlay choices. [1] [2] [3]

[github-actions]

Screenshot Changes

Base: 200fb2ed Current: 8be7deea

Changed (1)

editor/inlineCompletions/other/JumpToHint/Dark

Before	After

[Copilot]

Pull request overview

This PR refactors the Sessions/Agents chat input styling by removing experimental send-button hover/focus glow CSS, aiming to simplify and make the styling rules easier to maintain.

Changes:

• Removed hover/focus glow box-shadow rules for the experimental gradient send button.
• Removed now-unneeded transition: box-shadow declarations associated with the removed glow.