maybe a very strange question:

yesaaaaaa, now a borderline above the text / below the image then it is completely ok

You can add border to the text container by adding this CSS:

.gallery-item .gallery-caption {
    border-top: 1px solid red;
}

thanks Elvin

No problem. :D

that's what i want, thank you very much Elvin !!!!!
greeting Diedrich

that’s what i want, thank you very much Elvin !!!!!
greeting Diedrich

Nice one. No problem. :)