div.classname code example
Example 1: js add class
var element = document.getElementById('element');
element.classList.add('class-1');
element.classList.add('class-2', 'class-3');
element.classList.remove('class-3');
Example 2: html get class property
let element = document.querySelector('.preset');
let style = getComputedStyle(element);
let bg = style.backgroundColor;