Thanks Yigit! This was the solution.

Hi Yigit, i got the problem! The misrepresentation comes from the Browser-View-Size. If it is this not 100%, the ( + ) symbols where not displayed well (this is also fact on your demo-site). So, it is not cool but it is not a big fail.

Thanks for your help!

Hi Yigit, thank you for your answere. The strange thing is: the (+) elements are looking not the same at the same site.
So my question is: Is there a proofed way to style this elements?