diff --git a/frontend/src/components/modals/CustomStyleModal.tsx b/frontend/src/components/modals/CustomStyleModal.tsx
index 8504d81..c4d962f 100644
--- a/frontend/src/components/modals/CustomStyleModal.tsx
+++ b/frontend/src/components/modals/CustomStyleModal.tsx
@@ -1,4 +1,4 @@
-import { Fragment, useState, useCallback } from 'react'
+import { Fragment, useState, useEffect, useCallback } from 'react'
 import { toast } from 'sonner'
 import {
   Globe, Router, Network, Server, Layers, Box, Container, HardDrive,
@@ -160,7 +160,7 @@ function NodeEditor({ nodeType, style, onChange, onApplyToExisting }: NodeEditor
               min={0}
               step={10}
               value={style.width}
-              onChange={(e) => set('width', parseInt(e.target.value) || 0)}
+              onChange={(e) => set('width', parseInt(e.target.value, 10) || 0)}
               className="w-20 h-7 text-xs bg-[#0d1117] border border-[#30363d] rounded px-2 text-[#e6edf3]"
             />
           </div>
@@ -171,7 +171,7 @@ function NodeEditor({ nodeType, style, onChange, onApplyToExisting }: NodeEditor
               min={0}
               step={10}
               value={style.height}
-              onChange={(e) => set('height', parseInt(e.target.value) || 0)}
+              onChange={(e) => set('height', parseInt(e.target.value, 10) || 0)}
               className="w-20 h-7 text-xs bg-[#0d1117] border border-[#30363d] rounded px-2 text-[#e6edf3]"
             />
           </div>
@@ -285,14 +285,22 @@ export function CustomStyleModal({ open, onClose }: CustomStyleModalProps) {
     edges: { ...customStyle.edges },
   }))
 
-  const handleOpen = (isOpen: boolean) => {
-    if (isOpen) {
-      // Reset draft to current saved customStyle on open
+  // Reset the draft to the saved customStyle whenever the modal is (re)opened.
+  // The parent keeps this component mounted and only toggles `open`, so Radix's
+  // onOpenChange never fires for a parent-driven open — we key off the prop edge
+  // instead. Without this, abandoned edits (Cancel) would leak into the next open.
+  useEffect(() => {
+    if (open) {
       setDraft({ nodes: { ...customStyle.nodes }, edges: { ...customStyle.edges } })
       setSelection(null)
-    } else {
-      onClose()
     }
+    // Intentional snapshot-on-open: we don't want live customStyle changes to
+    // clobber an in-progress edit, only a fresh open should reset.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [open])
+
+  const handleOpen = (isOpen: boolean) => {
+    if (!isOpen) onClose()
   }
 
   const getNodeStyle = (t: NodeType): NodeTypeStyle =>
diff --git a/frontend/src/components/modals/__tests__/CustomStyleModal.test.tsx b/frontend/src/components/modals/__tests__/CustomStyleModal.test.tsx
index d368a87..13a4d47 100644
--- a/frontend/src/components/modals/__tests__/CustomStyleModal.test.tsx
+++ b/frontend/src/components/modals/__tests__/CustomStyleModal.test.tsx
@@ -134,4 +134,23 @@ describe('CustomStyleModal', () => {
     fireEvent.change(widthInputs[0], { target: { value: '250' } })
     expect((widthInputs[0] as HTMLInputElement).value).toBe('250')
   })
+
+  it('resets abandoned edits when reopened after cancel (mounted parent)', () => {
+    // Parent keeps the modal mounted and only toggles `open`, so the reset must
+    // happen on the open-prop edge, not via Radix onOpenChange.
+    const { rerender } = render(<CustomStyleModal open onClose={vi.fn()} />)
+    fireEvent.click(screen.getByRole('button', { name: 'Router' }))
+    const widthInput = screen.getAllByRole('spinbutton')[0]
+    fireEvent.change(widthInput, { target: { value: '250' } })
+    expect((widthInput as HTMLInputElement).value).toBe('250')
+
+    // Cancel = parent flips open → false, then later → true again.
+    rerender(<CustomStyleModal open={false} onClose={vi.fn()} />)
+    rerender(<CustomStyleModal open onClose={vi.fn()} />)
+
+    fireEvent.click(screen.getByRole('button', { name: 'Router' }))
+    const reopenedWidth = screen.getAllByRole('spinbutton')[0]
+    // Draft was reset to saved style (default width 0) — edit did not leak.
+    expect((reopenedWidth as HTMLInputElement).value).toBe('0')
+  })
 })