script.js

const darkColorsArr = [
 '#2C3E50',
 '#34495E',
 '#2C2C2C',
 '#616A6B',
 '#4A235A',
 '#2F4F4F',
 '#0E4B5A',
 '#36454F',
 '#2C3E50',
 '#800020',
];

function getRandomIndex() {
 const randomIndex = Math.floor(darkColorsArr.length * Math.random());
 return randomIndex;
}

const body = document.querySelector('body');
const bgHexCodeSpanElement = document.querySelector('#bg-hex-code');

function changeBackgroundColor() {
 const color = darkColorsArr[getRandomIndex()];

 bgHexCodeSpanElement.innerText = color;
 body.style.backgroundColor = color;
}
const btn = document.querySelector('#btn');

btn.onclick = changeBackgroundColor;