diff --git a/packages/query-devtools/src/__tests__/utils.test.ts b/packages/query-devtools/src/__tests__/utils.test.ts
index 1c30c5e918..30178af5ad 100644
--- a/packages/query-devtools/src/__tests__/utils.test.ts
+++ b/packages/query-devtools/src/__tests__/utils.test.ts
@@ -1,10 +1,12 @@
-import { describe, expect, it } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import {
+  convertRemToPixels,
   deleteNestedDataByPath,
   displayValue,
   getMutationStatusColor,
   getQueryStatusColorByLabel,
   getSidedProp,
+  setupStyleSheet,
   updateNestedDataByPath,
 } from '../utils'
 import type { MutationStatus } from '@tanstack/query-core'
@@ -846,4 +848,109 @@ describe('Utils tests', () => {
       expect(getSidedProp('padding', 'right')).toBe('paddingRight')
     })
   })
+
+  describe('convertRemToPixels', () => {
+    beforeEach(() => {
+      document.documentElement.style.fontSize = '16px'
+    })
+
+    afterEach(() => {
+      document.documentElement.style.fontSize = ''
+    })
+
+    it('should convert 1 rem to the document root font size in pixels', () => {
+      expect(convertRemToPixels(1)).toBe(16)
+    })
+
+    it('should return 0 for 0 rem', () => {
+      expect(convertRemToPixels(0)).toBe(0)
+    })
+
+    it('should multiply rem by the document root font size', () => {
+      expect(convertRemToPixels(2)).toBe(32)
+    })
+
+    it('should support decimal rem values', () => {
+      expect(convertRemToPixels(0.5)).toBe(8)
+    })
+
+    it('should reflect the current document root font size', () => {
+      document.documentElement.style.fontSize = '20px'
+      expect(convertRemToPixels(1)).toBe(20)
+    })
+
+    it('should support negative rem values', () => {
+      expect(convertRemToPixels(-1)).toBe(-16)
+    })
+
+    it('should support non-integer font sizes', () => {
+      document.documentElement.style.fontSize = '15.5px'
+      expect(convertRemToPixels(1)).toBe(15.5)
+    })
+  })
+
+  describe('setupStyleSheet', () => {
+    afterEach(() => {
+      document.head.querySelector('#_goober')?.remove()
+    })
+
+    it('should not insert any style tag when "nonce" is missing', () => {
+      setupStyleSheet()
+
+      expect(document.head.querySelector('#_goober')).toBeNull()
+    })
+
+    it('should not insert any style tag when "nonce" is an empty string', () => {
+      setupStyleSheet('')
+
+      expect(document.head.querySelector('#_goober')).toBeNull()
+    })
+
+    it('should append a style tag with id "_goober" to "document.head"', () => {
+      setupStyleSheet('test-nonce')
+
+      const styleTag = document.head.querySelector('#_goober')
+      expect(styleTag).not.toBeNull()
+      expect(styleTag?.tagName).toBe('STYLE')
+    })
+
+    it('should set the "nonce" attribute on the inserted style tag', () => {
+      setupStyleSheet('test-nonce')
+
+      expect(
+        document.head.querySelector('#_goober')?.getAttribute('nonce'),
+      ).toBe('test-nonce')
+    })
+
+    it('should not insert a duplicate style tag when "document.head" already has one', () => {
+      setupStyleSheet('first-nonce')
+      setupStyleSheet('second-nonce')
+
+      const styleTags = document.head.querySelectorAll('#_goober')
+      expect(styleTags).toHaveLength(1)
+      expect(styleTags[0]?.getAttribute('nonce')).toBe('first-nonce')
+    })
+
+    it('should append the style tag to the provided "ShadowRoot" target', () => {
+      const host = document.createElement('div')
+      const shadow = host.attachShadow({ mode: 'open' })
+
+      setupStyleSheet('test-nonce', shadow)
+
+      expect(shadow.querySelector('#_goober')).not.toBeNull()
+      expect(document.head.querySelector('#_goober')).toBeNull()
+    })
+
+    it('should not insert a duplicate style tag when the target already has one', () => {
+      const host = document.createElement('div')
+      const shadow = host.attachShadow({ mode: 'open' })
+
+      setupStyleSheet('first-nonce', shadow)
+      setupStyleSheet('second-nonce', shadow)
+
+      const styleTags = shadow.querySelectorAll('#_goober')
+      expect(styleTags).toHaveLength(1)
+      expect(styleTags[0]?.getAttribute('nonce')).toBe('first-nonce')
+    })
+  })
 })