Update mobile experience of underlined tabs

[kkartunov]

as per https://marvelapp.com/prototype/5bhjaie/screen/71551840

[kkartunov]

Tesing:
http://community-app.topcoder-dev.com/examples/contentful/viewport/3YZkRulnz4xBabdFPiVlZc
https://community-app.topcoder-dev.com/__community__/tco20/competition-overview/development/leaderboard

[SathyaJayabal]

verified on beta