Hi
Thanks for your feedback :-)
To use the mobile skin, you need to click on the "Mobile view" link, on the top left of the window (it's automatically loaded in a mobile/tablet device).
It's not recommended to change the skin in the "Settings > User Interface" menu, because it changes the user preference on each device, so keep your desktop theme here.
I think this might be the reason of your css problem. If not, what is the desktop theme you use ?