Thanks for Your help, so far. I really appreciate that.
I worked out the procedures You proposed. First I reinstalled the theme, second I switched off the the plug-ins. Furthermore I checked positive that I haven’t changed the CSS code or anything else.
At the end of the day these procedures showed up with no effect, that means that cloudero.de with Theme Intergalactic still comes up on iOS devices (esp. iPhone 5) with a too small layout.
If there is any more I could check that would be great.