feat(Button): add accept warning and danger button type

[Kimi-Gao]

First of all, thank you for your contribution! :-)

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Extra checklist:

elif isNewFeature :

• Update API docs for the component.
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• Add unit tests for the feature.

Relative issue:

#37

Description:

1. Adjust secondary button's background-color when hovering.
2. Add accept warning and danger button type.

ScreenShots: