Why isn't Javascript working when I use VSCode?

Hi everyone

I am working on the portfolio project for Javascript and I am going around the bend trying to work out why it is not working.

My index.html page has a link to main.js and then in the body of the page the following:

 <button id="test-button">This is a test</button>
        <p id="test-para">A test goes here</p>

Then in main.js I have the following:

let itemOne = document.querySelector("test-button");
let itemTwo = document.querySelector("test-para");

function changeBackground() {
    itemTwo.style.backgroundColor = "blue";

itemOne.addEventListener('click', changeBackground);

I have tried about fifty iterations of this and nothing is working. However, I know the Javascript file is linked properly because I can get it to display an alert window.

Any troubleshooting tips for this extraordinarily frustrated newbie?

If the script tag is before the body in the html, you may need to put the defer attribute in the script tag.