UI Style Inconsistency - Restyle the core-modal to make it conform to the design spec

[chaowentan]

The core modal should look like this:

https://drive.google.com/file/d/0B3sjMmpdLvk4Tzk4ZnJpUV9nSkE/view

[jonboiser]

@chaowentan The current core-modal also provides a '<-' back arrow button when back prop is provided. This is to support multi-step workflows inside a modal.

Does the new spec have any recommendations for placing this back control? I don't think I see any in the screenshots.

[chaowentan]

@jonboiser We would have to ask the design team for recommendation on that.

[indirectlylit]

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