Foreword

document.designMode, you can control the entire document to become editable.
We use "on" and "off" to adjust.
We can do many things through document.execCommand, for example: insertText.
 

Demo

Here is a simple demonstration for everyone to see ( 11 seconds ), The following demonstration is pure Look cool.
Paste the code, and you can edit the webpage. In the video, I adjusted the number of "stars".