How can I make it true??

Question

https://code.sololearn.com/Wc2Of4PSqzPx/?ref=app

Answer 1

Toni's change works or single line:
document.body.style.backgroundColor = document.getElementById("color").value;

Answer 2

The body in your CSS file is not defined.
Try this for example
body
{
background-color: blue;
}

Answer 3

Your body is not defined in javascript.

function a(){
var body = document.getElementsByTagName("body")[0];
body.style.backgroundColor = document.getElementById("color").value;
}
document.getElementById("btn").addEventListener("click" , a)

Answer 4

thank you