Using the right style/settings?

Hi,

On this ( https://graffitinetwerk.nl ) page i have 12 portfolio thumbnails at the bottom of the page.
If i understand the setup movie correctly the class to reach these images in is .work-item style-3

I tried these breaking points; 270, 281, 300, 352, 420 and 600

But nothing happens.
What am i doing wrong, could you help?
Hope to hear from you..

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