Some minor improvements

I was using this design as a target for practicing my analyzing skill, so I think I should go on and implement these improvements.

Each improvement is contained within a single commit, with my thought process explained in the comment.

Please take a look and give me your feedback. Our discussion here should also be useful for my future work on SmartTAB and FlavorPlease.

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Note: In Google's document there are 5 recommended shadow levels. I decided to skip level 1 because the effect is too small and hard to feel. The shadow hierarchy I used starts from level 2. This is indeed a personal decision and I would like to know what you think.