start game overlay resizes to gameboard

[EricSnell]

added just a single css prop to the board container to fix start game overlay not fitting to the gameboard

[coveralls]

Pull Request Test Coverage Report for Build 164

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 163:	0.0%
Covered Lines:	1164
Relevant Lines:	1164

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💛 - Coveralls

[turnerhayes]

Thanks for taking this on, Eric! Looks great!