Add possibility to set class names

[vladshcherbin]

Currently the classes are hardcoded, it would be great if we could change them.

[KyleAMathews]

What's your usecase?

[vladshcherbin]

@KyleAMathews we are using classes for styling and have a convention to name them as .headroom-unfixed.

[Benjamin-Dobell]

@KyleAMathews

What's your usecase?

As a general rule libraries (React or otherwise) shouldn't enforce global CSS names because:

• They can accidentally collide with the user's CSS names.
• Multiple instances of this library won't play nice e.g. If I were to ship a JS library for others to use and wrap it up nicely with webpack, if both the user and myself were to attempt to use react-headroom our styles would conflict.
• You can't have multiple instances of this component with different styles. Although, I do recognise that's unlikely with this particular component.
• If you want to do something dynamic, in general you can't easily/reliably dynamically modify global CSS - again, particularly if you're shipping a library.
• Most importantly, you can't use JSS.

The last point essentially makes this library incompatible with common theming engines found in libraries like material-ui, and is the issue I ran into.

I would appreciate it if you could review and ideally merge https://github.com/KyleAMathews/react-headroom/pull/124

[designbyadrian]

Please see react-autosuggest: https://github.com/moroshko/react-autosuggest#theme-prop

I'm using CSS Modules, which means that I currently have to put all headroom CSS styles in a global stylesheet, which I don't want. By being able to configure class names, I can keep the style definitions in my CSS module files.