Resizing the textarea by toggling classname off and on in React.js

Frst of here is my codepen

I accomplished changing the color of text of my toolbar when someone clicks on the toolbar That was my first time turning “On/Off” a class in React.

What my real goal is to resize the editor and previewer from its initial size to 100% as shown in freecodecamp example. Every time someone clicks on the edit icon on right hand side of my tool bar the texteditor or previewer should resize to 100%.

Please help