How to add and remove multiple CSS classes simultaneously from a DOM node

My very bad inking skills trying to create a medium blog post worthy image. I used a Faber-Castell fountain pen and Waterman Havana brown ink as only cool boys write with brown inks 🤣

Hello folks, here we are with another short story from the frontend world. We are going to learn how to add and remove multiple CSS classes from a DOM node, in our case a div.

The boring way 🤢