code for size of images on mobile

Site URL: https://stuwkrachtvier.squarespace.com/

Hi! 

I inserted an image that is very small on desktop but gets huge when I switch to mobile. 

Is there a way (with code for example) to make sure the images stay small on mobile as well? 

https://stuwkrachtvier.squarespace.com/ password: 4444

Thank you! 

I dont see images on above link. Can you share link to exact page?

Yes, ofcourse! Here you go https://stuwkrachtvier.squarespace.com/vierpijlers

2 hours ago, studioearl said:

Yes, ofcourse! Here you go https://stuwkrachtvier.squarespace.com/vierpijlers

Add to Home > Design > Custom CSS

@media screen and (max-width:767px) {
div#page-section-5f9be7dc6db28f187f485c16 .span-12>div:nth-child(-n+7) .image-block {
    width: 30% !important;
}
}

Thank you so much!