CSS - class applies on click [resolved]

I would like to apply a certain class to an object only when the object has been clicked on. I know you can do:

Code:

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#Obj:hover

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Which will apply that part of CSS to the object when the mouse is hovering over the object. Is there an equivalent to when you've clicked the object or do I have to write JavaScript to do the trick?

have you tried #Obj:active ?

That doesn't work exactly how I want it. But I've managed to make it in JavaScript now anyways. It's not quite a neat, but it works.
Thanks anyway.

edit: I'd never known about that action, thanks for pointing it out to me.