can someone help me with the site code?

I’m a beginner with codes, my thumbnails are 600px wide and high, but seeing the website code I find the code that is like element.style {
height: 628.391px;
}

this line inserted directly into the html is causing the thumbnail to have compromised resolution. I looked for some way to launch a css to overlay this code but I can’t find any way. Can someone help me?

The page I need help with: [log in to see the link]