Answers for "how to change styles of all elements js"

JS change styles

// select element from DOM
const sample = document.getElementById("myid");
// or you can use *vars*
var sample = document.getElementById("myid");

// change css style
sample.style.color = 'red'; // Change color
// or (not recomended)
sample.style = "color: red"; //This changes all styles. NOT RECOMENDED

adding styling to element using javascript

var elem = document.querySelector('#some-element');

// Set color to purple
elem.style.color = 'purple';

// Set the background color to a light gray
elem.style.backgroundColor = '#e5e5e5';

// Set the height to 150px
elem.style.height = '150px';