Why does ReactJs index page appear zoomed out?

I have noticed whenever I access the index route on a ReactJs web app, the page appears zoomed out. Whenever I access any of the other pages/routes, things appear normal sized.

I have now noticed that has happened across multiple ReactJs websites I've created. Why is this so? How can I stop this "zoomed out" behavior for these index pages?

For context, I am using Google Chrome.