// getElementById for id
// u can apply effect or whatever u want

// change #container background be dark
const background = document.getElementById('container');
background.style.background = '#333';

// change title h2 color be white, uppercase,padding
const title = document.getElementById('title');
title.style.color = '#fff';
title.style.textTransform = 'uppercase';
title.style.padding = '1.25rem';