Practising with the DOM tree from the Console

[m3g4p0p]

@assembly21

Is it because I’m in the console that I can’t select by class name and set an extra className?

No, it’s working in your code above because you’re setting the className of a specific element, namely document.getElementsByClassName('hot')[2], whereas in your OP you’re setting the className of an HTMLCollection. Have a look here for reference. :-)