Zeitreise, problem with featured image on portfolio templates page

HI, I’ve making my portfolio website using Zeitreise
and I know this theme is awesome.
anyway, I’ve checked .css and I don’t know how to set all the images on the portfolio page like its featured image.

I mean when I see your live demo page,
( http://themes.elmastudio.de/zeitreise/portfolio/create-your-own-dreams-by-ellen/ )
two below images’s width seems same with the featured image’s size.
but I can’t make it.

I did set my all images’s width 1280px on media library,
it does not work on portfolio page;

should I add any css code?
I did insert code the last Jan 20’s answer but nothing happened.

how can I make it better? thx :)