Simple WordPress Task: Update Plugin & Fix Menu Styling

I am looking for a WordPress expert to do a very quick, simple fix on my website. This should be a fast 15 to 30-minute task for someone who knows their way around WordPress. The Task: The main menu is dropping down behind the page content on mobile devices, and I need a quick CSS z-index fix. What I Need From You: You must be highly experienced with WordPress [and CSS/HTML if it's a styling issue]. Ability to jump in, fix the issue immediately, and verify that it works. No agency pitches or long cover letters, please—just let me know if you can fix this right now! Budget: This is a strict $10 fixed-price project for a very quick task. If you do this well and quickly, I will definitely keep you in mind for future quick fixes and give you a 5-star review. To Apply: Please start your proposal with the word "QUICK-FIX" and tell me how quickly you can get this done. Looking forward to getting this knocked out!