how to add css in classlist javascript code example

Example: add to classlist javascript

Add multiple classes to a 
 element:
document.getElementById("myDIV").classList.add("mystyle", "anotherClass", "thirdClass");

Remove a class from a 
 element:
document.getElementById("myDIV").classList.remove("mystyle");

Remove multiple classes from a 
 element:
document.getElementById("myDIV").classList.remove("mystyle", "anotherClass", "thirdClass");

Toggle between two classes for a 
 element:
document.getElementById("myDIV").classList.toggle("newClassName");

Find out if an element has a "mystyle" class:
document.getElementById("myDIV").classList.contains("mystyle");