Tweak content box on play info pages for mobile screens

[cmil]

On play info pages (e.g. https://staging.dracor.org/ger/lessing-emilia-galotti) the contents of the individual tabs is displayed in a box (#dashboard > div) hovering over main background. While I like the white background of that box, on narrow screens its margins, drop shadow and padding take quite some space that would better be used for the actual contents, especially the network graph and charts. Therefore, for mobile screens, I suggest to eliminate this box or make it use 100% of available width without drop shadow and margins and reduce its inner padding.

Alternatively we could consider getting rid of this box altogether, since it is kind of a remnant of the bootstrap card widget we used before but have more or less dissolved by now.