[$20] - Current challenges listing in Dashboard (mobile view)

[birdofpreyru]

This is how it looks now: challenge cards are the same large as in the Desktop view, and they layed out horizontallly, making it a bit uncomfortable to scroll around the page.

Let's make two changes for the mobile view:

1. Lay out challenge cards vertically, without a dedicated scrolling area. I.e. as we scroll the dashboard page down, the active challeges should be a part of the page flow.
2. Make the cards collapsable to the content. I.e. the main area should be as high, as the content is (which is the phase name, the counter of the time till the end of the current phase + some number of buttons + small padding above and below the content).

The changes you make should not impact the desktop view!