document style

// Here are two different ways
document.getElementById("myH1").style.color = "red";
element.style.backgroundColor = "red";   // set the background color of an element to red

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';

 document.getElementById("myH1").style.color = "red";