[Draft][Epic] Modernize Kibana visual language — EUI tokens & component defaults

[ryankeairns]

Summary

Expanded change list from the design exploration POC for scope discussion. This epic covers EUI-side work only: Borealis-delta tokens, then light component default shifts.

Not planned / prioritized yet. Values and behaviors below are illustrative of the proposed direction; they are not locked.

Kibana chrome/layout (nav, app header, headerless global header, product spacing props) is out of scope here — Shared UX / apps separately.

Dependency

1. Token updates first
2. Component issues can proceed in parallel once tokens exist

Sub-tasks

See below

Open decisions

1. Theme / delivery vehicle — new Borealis-derived theme vs iterate Borealis in place vs gated rollout (prefer token-driven usage; avoid long-lived theme === … forks)
2. Quieter edges — keep real 1px borders (optionally quieter color), or move edged surfaces (esp. Panel / forms) to a faux border (box-shadow: 0 0 0 1px …) for a softer edge. Pick one edge system.
3. EuiText default → subdued — yes/no; EuiText only vs also EuiTextColor’s default
4. Third surface token — new semantic (e.g. backgroundBaseRecessed / subtle) vs reuse subdued
5. One size of buttons/inputs (small) — adopt or keep multiple sizes
6. EUI spacing migration — wire component padding/gaps to spacing.* aliases (e.g. spacing.panelInset, spacing.pageInset, spacing.controlsGap) and clean up legacy padding props in foundation vs follow-on

Related (not EUI)

• Workspace on canvas, nav + side panel, app header, headerless primary nav
• Dashboard / Discover / query-bar spacing and surface tweaks