When reading your Gmail emails, you might have an issue where they are too small, and you need to zoom in or too large and you want to zoom out. If you zoom in and out using your browser zoom feature or hold down the Ctrl key and scroll with your mouse wheel, you will notice that the entire page zooms in and out and not just the email itself.
There is a free extension you can use for Chrome or Edge that will allow you to zoom in and out of the body of the Gmail email itself and not the rest of the page. It's very easy to use and simple to install.