diff --git a/frontend/components/Scanner.tsx b/frontend/components/Scanner.tsx
index 6d9904aa..fb07e822 100644
--- a/frontend/components/Scanner.tsx
+++ b/frontend/components/Scanner.tsx
@@ -236,7 +236,12 @@ export default function Scanner({ onScanSuccess, onOCRMatch, paused }: ScannerPr
         {isSelecting && capturedImage && (
           <div className="absolute inset-0 z-50 bg-slate-950 flex flex-col">
             <div className="relative flex-1 bg-black flex items-center justify-center overflow-hidden">
-               <img src={capturedImage || undefined} className="max-w-full max-h-full object-contain" id="ocr-canvas-preview" />
+               <img
+                 src={capturedImage || undefined}
+                 className="max-w-full max-h-full object-contain"
+                 id="ocr-canvas-preview"
+                 alt="OCR text detection preview with detected words highlighted"
+               />
                <div className="absolute inset-0 flex items-center justify-center">
                   <div className="relative" style={{ width: '100%', height: '100%' }}>
                     {detectedWords.map((w, i) => (
diff --git a/frontend/styles/DESIGN_SYSTEM.md b/frontend/styles/DESIGN_SYSTEM.md
new file mode 100644
index 00000000..516904e2
--- /dev/null
+++ b/frontend/styles/DESIGN_SYSTEM.md
@@ -0,0 +1,238 @@
+# TFM aInventory Design System
+
+## Z-Index Scale
+
+Explicit z-index layering for consistent stacking context.
+
+```
+z-10   = Local stacking (shadows, hover states)
+z-20   = Cards, modals (low-level)
+z-30   = Dropdowns, tooltips
+z-40   = Fixed navigation (BottomNav)
+z-50   = Full-screen overlays (Scanner, AIOnboarding)
+z-[100] = Toast notifications, alerts
+```
+
+### Applied Locations:
+- `z-10`: Interactive states, hover effects
+- `z-20`: Modal backgrounds, card borders
+- `z-40`: BottomNav fixed footer
+- `z-50`: Scanner.tsx, AIOnboarding.tsx, full-screen UI
+- `z-[100]`: Toast messages (react-hot-toast)
+
+---
+
+## Spacing Scale
+
+All spacing follows a consistent 4px baseline.
+
+```
+4px   = gap-1 (tightest)
+8px   = gap-2
+12px  = gap-3
+16px  = gap-4 (default)
+24px  = gap-6
+32px  = gap-8
+48px  = gap-12
+64px  = gap-16
+```
+
+### Applied Pattern:
+- Use `gap-` utilities for sibling spacing
+- Use `p-` for padding on containers
+- Use `m-` sparingly (prefer gap)
+- Never use arbitrary spacing (e.g., no `gap-[13px]`)
+
+---
+
+## Opacity Scale for Backgrounds
+
+Consistent opacity for glass/translucent effects.
+
+```
+bg-slate-950/40   = Light transparency (hover states)
+bg-slate-950/60   = Medium transparency (overlays)
+bg-slate-950/80   = Heavy transparency (backdrop blur)
+bg-slate-900/40   = Light glass (cards)
+bg-slate-900/50   = Medium glass (borders)
+bg-slate-900/90   = Heavy glass (panels)
+```
+
+### Applied Locations:
+- `/40`: Hover states, subtle layers
+- `/50`: Card backgrounds
+- `/60-80`: Modal backdrops
+- `/90`: Solid-looking panels with slight transparency
+
+---
+
+## Transition Timing
+
+All interactive elements use consistent easing and duration.
+
+```
+transition-colors     = color changes (150ms)
+transition-all        = all properties (200-300ms)
+active:scale-95       = click feedback
+hover:opacity-80      = hover feedback
+```
+
+### Standards:
+- Button state changes: `transition-colors duration-200`
+- Major layout changes: `transition-all duration-300`
+- Never use `duration-0` or `duration-1000` without reason
+- Focus states: instant (no transition on ring)
+
+---
+
+## Focus States
+
+All interactive elements must be keyboard accessible.
+
+```
+focus:ring-2            = visible focus indicator
+focus:ring-primary      = brand color on interactive elements
+focus:ring-blue-500     = alternate for secondary buttons
+focus:outline-none      = removes browser default
+```
+
+### Applied to:
+- All `<button>` elements
+- All `<a>` elements (links)
+- Form inputs (`<input>`, `<textarea>`, `<select>`)
+- Custom interactive components (role="button", tabIndex)
+
+---
+
+## Cursor States
+
+Interactive elements must signal affordance.
+
+```
+cursor-pointer      = clickable button/card
+cursor-not-allowed  = disabled state
+cursor-default      = non-interactive
+```
+
+### Applied Pattern:
+```jsx
+<button className="cursor-pointer hover:... focus:ring-2 disabled:cursor-not-allowed">
+  Action
+</button>
+```
+
+---
+
+## Contrast Requirements
+
+All text must meet WCAG AA minimum 4.5:1 contrast ratio.
+
+### Light Mode (if implemented):
+- Body text: `text-slate-900` (#0F172A) on white
+- Secondary: `text-slate-600` (#475569) on white
+- Muted: `text-slate-500` (#64748B) on white (only for labels)
+
+### Dark Mode (current):
+- Body text: `text-white` on dark bg
+- Secondary: `text-slate-300` (#CBD5E1) on dark bg
+- Muted: `text-slate-500` (#64748B) on dark bg
+
+### Verified Combinations:
+- ✓ white text on bg-slate-950
+- ✓ text-slate-300 on bg-slate-900/50
+- ✓ text-primary (#3B82F6) on dark backgrounds
+
+---
+
+## Button States
+
+Every button must implement all required states.
+
+```jsx
+<button
+  className="
+    /* Default */
+    bg-primary text-white rounded-lg font-semibold
+    /* Hover */
+    hover:bg-blue-600
+    /* Focus */
+    focus:ring-2 focus:ring-blue-500 focus:outline-none
+    /* Active */
+    active:scale-95
+    /* Disabled */
+    disabled:opacity-50 disabled:cursor-not-allowed
+    /* Transition */
+    transition-all duration-200
+  "
+  disabled={isLoading}
+>
+  Action
+</button>
+```
+
+---
+
+## Icon Guidelines
+
+- All icons from Lucide React (size 16-24)
+- Never use emoji as UI icons
+- Icon-only buttons require `aria-label`
+- Icon size: `size={20}` (default), `size={16}` (compact), `size={24}` (prominent)
+
+---
+
+## Form Elements
+
+All form inputs require:
+1. Associated `<label>` with `htmlFor` attribute
+2. Clear focus states
+3. Helpful placeholder text (optional, don't replace label)
+4. Validation feedback
+
+```jsx
+<label htmlFor="email" className="block text-sm font-semibold mb-2">
+  Email Address
+</label>
+<input
+  id="email"
+  type="email"
+  placeholder="you@example.com"
+  className="
+    w-full px-3 py-2 bg-slate-800 border border-slate-700 rounded-lg
+    text-white placeholder:text-slate-500
+    focus:border-primary focus:ring-2 focus:ring-primary
+    transition-colors duration-200
+  "
+/>
+```
+
+---
+
+## Modal/Overlay Hierarchy
+
+Predictable layering for overlays.
+
+```
+z-40  = BottomNav (fixed)
+z-50  = Full-screen overlays (Scanner, AIOnboarding)
+z-50+ = Nested modals (ConfirmationModal, ItemComparisonModal)
+```
+
+Backdrop colors:
+- Scanner/AIOnboarding: `bg-slate-950` (opaque)
+- Modals: `bg-black/40` (semi-transparent)
+
+---
+
+## Migration Checklist
+
+When implementing these standards:
+
+- [ ] Add z-index only when necessary (nesting depth issue)
+- [ ] Use spacing scale utilities (no arbitrary values)
+- [ ] Add focus states to ALL interactive elements
+- [ ] Add cursor-pointer to all clickable elements
+- [ ] Verify transition duration is 150-300ms
+- [ ] Test keyboard navigation (Tab, Enter, Escape)
+- [ ] Verify contrast ratios (4.5:1 minimum)
+- [ ] Check reduced motion preferences (`prefers-reduced-motion`)