Deactivate "element.style" in css/html?

I see this css code in the "style" tab of the Chrome developer tools window:

element.style {
    height: auto;
    width: 100%;
    margin-top: -148px;
}

I want to overwrite it with this css code in my .css file:

.so-widget-sow-simple-masonry-simple-masonry-d75171398898 .sow-masonry-grid-item img {
    width: auto;
    height: 244px;
    margin-top: 0px;
    margin-left: auto;
    margin-right: auto; 
}

But the style definitions of the element.style is already there. I cant find the .js so fast. Can someone help me? Thx