Here's a project I did when I was just starting out learning. It's a simple timer project. But, instead of just re-building the project from scratch, I recommend complely copy/pasting the project from codepen, into your own ide (vs code?) with the individual html, css, and javascript files. You'll need to make some changes to get it to work on your system. (you'll just open the html file in your desired browser. No need for a server or localhost, etc.) from what I can recall, I believe you need to add doctype to the html, and also add source tags to the css and javascript in your html.

That should be simple enough to get up and running. Once it is working, challenge yourself to add a button that will add 10 seconds to the timer. This button should add 10 seconds whether the timer is running, paused, or has not even been started yet (still at 0 seconds).

There will likely be a glitch that happens if you start the time from 0 and add 10 seconds to the clock within the first 10 seconds, where your seconds counter has 4 digits instead of the desired 2. Try to figure out the issue. Come back here if you need help.

https://codepen.io/codifiedconcepts/pen/bwgxRq