diff --git a/theme.css b/theme.css
index 57eaf10..93a34e9 100644
--- a/theme.css
+++ b/theme.css
@@ -95,6 +95,16 @@
     --syntax-function: oklch(0.48 0.18 235);
     --syntax-type: oklch(0.48 0.14 195);
 
+    /* ── Chat surfaces ──
+     * Contract for lib-agent-chat-ui / lib-agent-dock-ui. User bubble is
+     * a filled, deep, high-contrast panel with light text; assistant
+     * bubble is a card-like surface with a hairline border. */
+    --chat-user-bg: oklch(0.48 0.2 295);
+    --chat-user-fg: oklch(1 0 0);
+    --chat-assistant-bg: oklch(1 0 0 / 0.7);
+    --chat-assistant-fg: oklch(0.16 0.025 285);
+    --chat-assistant-border: oklch(0 0 0 / 0.09);
+
     /* ── Radius ── Generous, premium feel. */
     --radius: 1rem;
 
@@ -218,6 +228,13 @@
     --syntax-function: oklch(0.78 0.16 235);
     --syntax-type: oklch(0.78 0.14 195);
 
+    /* ── Chat surfaces (dark) ── */
+    --chat-user-bg: oklch(0.54 0.2 295);
+    --chat-user-fg: oklch(1 0 0);
+    --chat-assistant-bg: oklch(0.24 0.04 290 / 0.7);
+    --chat-assistant-fg: oklch(0.97 0.005 280);
+    --chat-assistant-border: oklch(1 0 0 / 0.1);
+
     --elevation-1: 0 1px 2px oklch(0 0 0 / 0.4);
     --elevation-2: 0 2px 8px oklch(0 0 0 / 0.4), 0 1px 2px oklch(0 0 0 / 0.3);
     --elevation-3: 0 4px 16px oklch(0 0 0 / 0.45), 0 2px 4px oklch(0 0 0 / 0.3);