diff --git a/frontend/src/components/MarkdownFormatToolbar.tsx b/frontend/src/components/MarkdownFormatToolbar.tsx
new file mode 100644
index 0000000..d9ca1d0
--- /dev/null
+++ b/frontend/src/components/MarkdownFormatToolbar.tsx
@@ -0,0 +1,160 @@
+/**
+ * MarkdownFormatToolbar — contextual toolbar for selected markdown cards.
+ * Shows background color picker, width presets, and accent color picker.
+ */
+
+import React, { useState, useEffect } from 'react';
+
+interface MarkdownFormatToolbarProps {
+  x: number;
+  y: number;
+  bgColor: string;
+  accentColor: string;
+  width: number;
+  onBgColorChange: (color: string) => void;
+  onAccentColorChange: (color: string) => void;
+  onWidthChange: (width: number) => void;
+}
+
+const PRESET_COLORS = [
+  '#232336', '#1e1e2e', '#2a2a3a', '#1a2332', '#2a1a2a',
+  '#1a2a1a', '#2a2a1a', '#333333', '#1a1a1a', '#3a2a42',
+];
+
+const ACCENT_COLORS = [
+  '#7950f2', '#4dabf7', '#69db7c', '#ffd43b', '#ff6b6b',
+  '#e64980', '#ffa94d', '#868e96', '#ffffff', '#f783ac',
+];
+
+const WIDTH_PRESETS = [
+  { label: 'S', value: 300 },
+  { label: 'M', value: 450 },
+  { label: 'L', value: 650 },
+];
+
+export default function MarkdownFormatToolbar(props: MarkdownFormatToolbarProps) {
+  const { x, y, bgColor, accentColor, width, onBgColorChange, onAccentColorChange, onWidthChange } = props;
+  const [showBgPicker, setShowBgPicker] = useState(false);
+  const [showAccentPicker, setShowAccentPicker] = useState(false);
+
+  useEffect(() => {
+    const onDown = () => { setShowBgPicker(false); setShowAccentPicker(false); };
+    window.addEventListener('pointerdown', onDown);
+    return () => window.removeEventListener('pointerdown', onDown);
+  }, []);
+
+  const btnStyle: React.CSSProperties = {
+    display: 'flex', alignItems: 'center', justifyContent: 'center',
+    height: '26px', background: 'transparent', border: 'none', borderRadius: '5px',
+    color: '#999', cursor: 'pointer', padding: '0 6px', fontSize: '11px',
+    fontFamily: 'system-ui, sans-serif', whiteSpace: 'nowrap', transition: 'all 0.1s',
+  };
+
+  return (
+    <div
+      style={{
+        position: 'absolute', left: x, top: y - 8,
+        transform: 'translate(-50%, -100%)',
+        display: 'flex', alignItems: 'center', gap: '1px', padding: '3px',
+        background: 'rgba(22, 22, 22, 0.96)', border: '1px solid #333',
+        borderRadius: '10px', backdropFilter: 'blur(12px)',
+        boxShadow: '0 4px 20px rgba(0,0,0,0.5)', zIndex: 100, pointerEvents: 'auto',
+      }}
+      onPointerDown={(e) => e.stopPropagation()}
+    >
+      {/* Background color */}
+      <div style={{ position: 'relative' }}>
+        <button
+          style={{ ...btnStyle, width: '26px', padding: 0 }}
+          onClick={(e) => { e.stopPropagation(); setShowBgPicker((v) => !v); setShowAccentPicker(false); }}
+          title="Card background"
+        >
+          <div style={{ width: '14px', height: '14px', borderRadius: '3px', background: bgColor, border: '1px solid #555' }} />
+        </button>
+        {showBgPicker && (
+          <div
+            style={{
+              position: 'absolute', top: '100%', right: 0, marginTop: '4px',
+              background: 'rgba(22, 22, 22, 0.98)', border: '1px solid #333',
+              borderRadius: '8px', padding: '8px', zIndex: 200,
+              boxShadow: '0 4px 16px rgba(0,0,0,0.5)',
+            }}
+            onPointerDown={(e) => e.stopPropagation()}
+          >
+            <div style={{ display: 'grid', gridTemplateColumns: 'repeat(5, 1fr)', gap: '4px' }}>
+              {PRESET_COLORS.map((c) => (
+                <button
+                  key={c}
+                  onClick={() => { onBgColorChange(c); setShowBgPicker(false); }}
+                  style={{
+                    width: '22px', height: '22px', borderRadius: '4px', background: c,
+                    border: c === bgColor ? '2px solid #4a90d9' : '1px solid #444',
+                    cursor: 'pointer', padding: 0,
+                  }}
+                />
+              ))}
+            </div>
+          </div>
+        )}
+      </div>
+
+      <div style={{ width: '1px', height: '18px', background: '#333', margin: '0 2px', flexShrink: 0 }} />
+
+      {/* Width presets */}
+      <div style={{ display: 'flex', gap: '1px' }}>
+        {WIDTH_PRESETS.map((p) => (
+          <button
+            key={p.label}
+            style={{
+              ...btnStyle, width: '24px', padding: 0,
+              color: Math.abs(width - p.value) < 30 ? '#fff' : '#666',
+              background: Math.abs(width - p.value) < 30 ? '#444' : 'transparent',
+            }}
+            onClick={() => onWidthChange(p.value)}
+            title={`${p.label} (${p.value}px)`}
+          >
+            {p.label}
+          </button>
+        ))}
+      </div>
+
+      <div style={{ width: '1px', height: '18px', background: '#333', margin: '0 2px', flexShrink: 0 }} />
+
+      {/* Accent color */}
+      <div style={{ position: 'relative' }}>
+        <button
+          style={{ ...btnStyle, width: '26px', padding: 0 }}
+          onClick={(e) => { e.stopPropagation(); setShowAccentPicker((v) => !v); setShowBgPicker(false); }}
+          title="Accent color"
+        >
+          <div style={{ width: '14px', height: '14px', borderRadius: '6px', background: accentColor, border: '1px solid #555' }} />
+        </button>
+        {showAccentPicker && (
+          <div
+            style={{
+              position: 'absolute', top: '100%', right: 0, marginTop: '4px',
+              background: 'rgba(22, 22, 22, 0.98)', border: '1px solid #333',
+              borderRadius: '8px', padding: '8px', zIndex: 200,
+              boxShadow: '0 4px 16px rgba(0,0,0,0.5)',
+            }}
+            onPointerDown={(e) => e.stopPropagation()}
+          >
+            <div style={{ display: 'grid', gridTemplateColumns: 'repeat(5, 1fr)', gap: '4px' }}>
+              {ACCENT_COLORS.map((c) => (
+                <button
+                  key={c}
+                  onClick={() => { onAccentColorChange(c); setShowAccentPicker(false); }}
+                  style={{
+                    width: '22px', height: '22px', borderRadius: '4px', background: c,
+                    border: c === accentColor ? '2px solid #4a90d9' : '1px solid #444',
+                    cursor: 'pointer', padding: 0,
+                  }}
+                />
+              ))}
+            </div>
+          </div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/pages/Editor.tsx b/frontend/src/pages/Editor.tsx
index 8828c4a..e03503a 100644
--- a/frontend/src/pages/Editor.tsx
+++ b/frontend/src/pages/Editor.tsx
@@ -44,6 +44,7 @@ import * as ops from '../canvas/operations';
 import ReactDOM from 'react-dom';
 import MarkdownReadView from '../components/MarkdownReadView';
 import PasteChoicePopup from '../components/PasteChoicePopup';
+import MarkdownFormatToolbar from '../components/MarkdownFormatToolbar';
 const LazyMarkdownEditView = React.lazy(() => import('../components/MarkdownEditView'));
 
 // Hooks
@@ -133,6 +134,7 @@ export default function Editor({ isPublicView }: EditorProps) {
   >(null);
   const [videoCtrl, setVideoCtrl] = useState<{ videoSprite: VideoSprite; screenRect: { x: number; y: number; w: number; h: number } } | null>(null);
   const [pastePopup, setPastePopup] = useState<{ x: number; y: number; text: string; html: string; hasImage: boolean } | null>(null);
+  const [mdToolbar, setMdToolbar] = useState<{ x: number; y: number; item: SceneItem } | null>(null);
   const [showMinimap, setShowMinimap] = useState(true);
   const [minimapData, setMinimapData] = useState<{ items: any[]; viewportBounds: any; contentBounds: any }>({
     items: [], viewportBounds: { x: 0, y: 0, w: 1, h: 1 }, contentBounds: { x: 0, y: 0, w: 1, h: 1 },
@@ -708,6 +710,17 @@ export default function Editor({ isPublicView }: EditorProps) {
       setTextToolbar(null);
     }
 
+    // Markdown format toolbar: show when exactly one markdown card is selected
+    const mdItems = items.filter((it) => it.type === 'markdown');
+    if (mdItems.length === 1 && items.length === 1) {
+      const b = getItemWorldBounds(mdItems[0]);
+      const screenTL = vp.toScreen(b.x, b.y);
+      const screenTR = vp.toScreen(b.x + b.w, b.y);
+      setMdToolbar({ x: (screenTL.x + screenTR.x) / 2, y: screenTL.y, item: mdItems[0] });
+    } else {
+      setMdToolbar(null);
+    }
+
     if (items.length < 2) { setSelToolbar(null); } else {
       // Compute world bounding box of selection
       let minX = Infinity, minY = Infinity, maxX = -Infinity;
@@ -1066,6 +1079,31 @@ export default function Editor({ isPublicView }: EditorProps) {
           />
         )}
 
+        {/* Markdown format toolbar */}
+        {mdToolbar && activeTool === ToolType.SELECT && !contextMenu && !editingMdId && (
+          <MarkdownFormatToolbar
+            x={mdToolbar.x}
+            y={mdToolbar.y}
+            bgColor={(mdToolbar.item.data as MarkdownObject).bgColor}
+            accentColor={(mdToolbar.item.data as MarkdownObject).accentColor}
+            width={mdToolbar.item.data.w}
+            onBgColorChange={(color) => {
+              (mdToolbar.item.data as MarkdownObject).bgColor = color;
+              onCanvasChange([mdToolbar.item.id]);
+            }}
+            onAccentColorChange={(color) => {
+              (mdToolbar.item.data as MarkdownObject).accentColor = color;
+              onCanvasChange([mdToolbar.item.id]);
+            }}
+            onWidthChange={(w) => {
+              mdToolbar.item.data.w = w;
+              onCanvasChange([mdToolbar.item.id]);
+              mdOverlay?.measureHeight(mdToolbar.item.id);
+              selectionRef.current?.transformBox.update([mdToolbar.item]);
+            }}
+          />
+        )}
+
         {/* Video controls (floating, below selected video) */}
         {videoCtrl && activeTool === ToolType.SELECT && !contextMenu && (
           <VideoControls