diff --git a/app/[workspace]/project/[projectId]/design/page.tsx b/app/[workspace]/project/[projectId]/design/page.tsx
index b17c38c..72df47c 100644
--- a/app/[workspace]/project/[projectId]/design/page.tsx
+++ b/app/[workspace]/project/[projectId]/design/page.tsx
@@ -553,6 +553,7 @@ export default function DesignPage({
   const [surfaces, setSurfaces] = useState<string[]>([]);
   const [surfaceThemes, setSurfaceThemes] = useState<Record<string, string>>({});
   const [selectedThemes, setSelectedThemes] = useState<Record<string, string>>({});
+  const [activeSurfaceId, setActiveSurfaceId] = useState<string | null>(null);
   const [savingLock, setSavingLock] = useState<string | null>(null);
   const [savingSurfaces, setSavingSurfaces] = useState(false);
   const [loading, setLoading] = useState(true);
@@ -561,9 +562,11 @@ export default function DesignPage({
     fetch(`/api/projects/${projectId}/design-surfaces`)
       .then(r => r.json())
       .then(d => {
-        setSurfaces(d.surfaces ?? []);
+        const loaded = (d.surfaces ?? []) as string[];
+        setSurfaces(loaded);
         setSurfaceThemes(d.surfaceThemes ?? {});
         setSelectedThemes(d.surfaceThemes ?? {});
+        if (loaded.length > 0) setActiveSurfaceId(loaded[0]);
       })
       .catch(() => toast.error("Failed to load design data"))
       .finally(() => setLoading(false));
@@ -579,6 +582,7 @@ export default function DesignPage({
       });
       if (!res.ok) throw new Error();
       setSurfaces(ids);
+      setActiveSurfaceId(ids[0] ?? null);
       toast.success("Surfaces saved");
     } catch {
       toast.error("Failed to save surfaces");
@@ -619,7 +623,7 @@ export default function DesignPage({
 
   if (loading) {
     return (
-      <div className="flex items-center justify-center py-32">
+      <div className="flex items-center justify-center h-full">
         <Loader2 className="h-7 w-7 animate-spin text-muted-foreground" />
       </div>
     );
@@ -634,51 +638,74 @@ export default function DesignPage({
     );
   }
 
-  // Phase 2 — surfaces set, pick themes
+  // Phase 2 — left nav + main content
   const activeSurfaces = ALL_SURFACES.filter(s => surfaces.includes(s.id));
+  const currentSurface = activeSurfaces.find(s => s.id === activeSurfaceId) ?? activeSurfaces[0];
   const lockedCount = Object.keys(surfaceThemes).length;
 
   return (
-    <div className="space-y-10 p-6 max-w-5xl mx-auto">
-      <div className="flex items-start justify-between">
-        <div>
-          <h1 className="text-xl font-bold">Design</h1>
-          <p className="text-sm text-muted-foreground mt-0.5">
-            Choose a UI library for each surface — the AI coder will reference these when building.
-          </p>
+    <div className="flex h-full">
+      {/* Left nav */}
+      <div className="w-52 shrink-0 border-r flex flex-col">
+        <div className="px-4 py-4 border-b">
+          <p className="text-xs font-semibold text-muted-foreground uppercase tracking-wide">Surfaces</p>
         </div>
-        <div className="flex items-center gap-2">
+
+        <nav className="flex-1 py-2">
+          {activeSurfaces.map(surface => {
+            const Icon = surface.icon;
+            const isActive = surface.id === currentSurface?.id;
+            const isLocked = !!surfaceThemes[surface.id];
+            return (
+              <button
+                key={surface.id}
+                onClick={() => setActiveSurfaceId(surface.id)}
+                className={cn(
+                  "flex items-center gap-2.5 w-full px-4 py-2.5 text-left transition-colors relative",
+                  isActive
+                    ? "bg-muted text-foreground"
+                    : "text-muted-foreground hover:text-foreground hover:bg-muted/50"
+                )}
+              >
+                {isActive && (
+                  <div className="absolute left-0 top-1/2 -translate-y-1/2 h-6 w-0.5 bg-foreground rounded-r" />
+                )}
+                <Icon className="h-4 w-4 shrink-0" />
+                <span className="text-sm font-medium flex-1 truncate">{surface.name}</span>
+                {isLocked && <Lock className="h-3 w-3 shrink-0 text-muted-foreground" />}
+              </button>
+            );
+          })}
+        </nav>
+
+        <div className="px-4 py-3 border-t space-y-2">
           {lockedCount === activeSurfaces.length && lockedCount > 0 && (
-            <Badge variant="default" className="gap-1.5">
-              <Lock className="w-3 h-3" />
-              All locked in
-            </Badge>
+            <p className="text-[10px] text-muted-foreground flex items-center gap-1">
+              <CheckCircle2 className="h-3 w-3" /> All surfaces locked
+            </p>
           )}
-          <Button
-            variant="outline"
-            size="sm"
+          <button
             onClick={() => setSurfaces([])}
-            className="text-xs"
+            className="text-[11px] text-muted-foreground hover:text-foreground transition-colors"
           >
-            Change surfaces
-          </Button>
+            + Edit surfaces
+          </button>
         </div>
       </div>
 
-      <div className="space-y-10 divide-y divide-border">
-        {activeSurfaces.map((surface, i) => (
-          <div key={surface.id} className={i > 0 ? "pt-10" : ""}>
-            <SurfaceSection
-              surface={surface}
-              selectedThemeId={selectedThemes[surface.id] ?? null}
-              lockedThemeId={surfaceThemes[surface.id] ?? null}
-              onSelect={themeId => setSelectedThemes(prev => ({ ...prev, [surface.id]: themeId }))}
-              onLock={() => handleLock(surface.id)}
-              onUnlock={() => handleUnlock(surface.id)}
-              saving={savingLock === surface.id}
-            />
-          </div>
-        ))}
+      {/* Main content */}
+      <div className="flex-1 overflow-y-auto p-8">
+        {currentSurface && (
+          <SurfaceSection
+            surface={currentSurface}
+            selectedThemeId={selectedThemes[currentSurface.id] ?? null}
+            lockedThemeId={surfaceThemes[currentSurface.id] ?? null}
+            onSelect={themeId => setSelectedThemes(prev => ({ ...prev, [currentSurface.id]: themeId }))}
+            onLock={() => handleLock(currentSurface.id)}
+            onUnlock={() => handleUnlock(currentSurface.id)}
+            saving={savingLock === currentSurface.id}
+          />
+        )}
       </div>
     </div>
   );