Enhance Typing Practice Web App -- 2

I have a small typing-practice site running at https://typing-master-p3q8.onrender.com. The core purpose is crystal clear: help visitors increase their typing speed. Right now the experience is extremely bare-bones, so I’d like a developer who can focus on tightening one key capability—clean, reliable timed typing tests.

What I need from you
• Build (or rebuild) the timed test component so users can choose a length—30 s, 60 s, 2 min—and immediately see WPM, accuracy, and an error count when the clock hits zero.
• Store the result locally in the browser so the user can compare their last five scores without an account.
• Make sure the interface looks clean on desktop and mobile; a simple, distraction-free layout is fine as long as it scales.

Tech stack is flexible, but the existing front end is vanilla JavaScript served through an Express backend on Render, so sticking with JS/HTML/CSS—or React if you prefer—will keep deployment straightforward. Please keep the current URL structure intact so I can push straight to Render once you’re done.

Acceptance criteria
1. Timer starts on first keystroke and stops automatically at the chosen interval.
2. Results panel immediately shows WPM, accuracy %, total keystrokes, and backspace count.
3. Last five results persist with localStorage and clear correctly when the user clicks “Reset history.”
4. Page passes Lighthouse performance ≥ 90 on mobile.
5. Code is delivered through GitHub with a short README explaining build and deploy steps.

If this initial improvement goes smoothly, there’s room to layer in lessons, difficulty levels, and full user accounts later. Let me know how you’d tackle the timed test feature and roughly how long you’d need.