[react-scripts] template: given 100% width/height to react app container(<div id="root">)

Created by: ryota-murakami

What's the Improve

Currently, react app container dom document.getElementById('root') has only contents' height.

Current

↑dom height not covered browser screen empty space.

But generally, I suppose majority users will remove existing App component stuff(code, logo, css), and then start write their own component. At that time, if document.getElementById('root') has fullscreen width/height by already, initial develop feel is quite good I think.

PR applied

Samary

I'm glad anyone in the maintainer has read through, If this change is attractive to many users, that's would be great to merge and I'd like to contribute to improving create-react-app😀