Make all classnames overwritable

[loominade]

Since I am using BEM in my project, I am required to overwrite all the classnames defined in SlideDown. So I added these two new props:

import 'mything.css'

<SlideDown
  className='mything'
  transitioningClassName='mything--transitioning'
  closedClassName='mything--closed'
  closed={isMyThingClosed?}
>

If ommited, everything behaves as it did.

[JPeer264]

Nice addition. Wouldn't it be easier to read if it's passed via an object? Like so:

import 'mything.css'

<SlideDown
  className='mything'
  classNames={{
    transitioning: 'mything--transitioning',
    closed: 'mything--closed',
  }}
  closed={isMyThingClosed?}
>