Find the parent css and change the code inside it [Wordpress]

I am new website developer and even newer to Wordpress. I have a bug which is on this page.

You can see that the images have an opacity of 0.3 and that is because the parent div has a style that says opacity: 0.3. My question is how I can find that code in my files so I can remove the opacity and give it an opacity of 1 instead of 0.3.

This is a plugin called Sizron Facebook Album and the theme I am using called the7. The problem is probably from the7 theme as when I switched to an old theme, there wasn't a problem.

Note: I tried to add in my style.css an opacity:1; for the .image_wrapper, the div and the image but didn't work.

Would highly appreciate anyone that guides me on how should I look for file I need to edit.

Thanks in advance for everybody :)

via Chebli Mohamed