[pouta]

Can you explain a bit further what the code you posted does?

[msimpson]

Element.classList:

https://developer.mozilla.org/en-US/docs/Web/API/Element/cla...

Property Accessors (Bracket Notation):

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

Conditional (ternary) Operator:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...