Blog Post Backgrounds Transparent

I’m using the plug-in Simple Full Screen Background Image so that my image will fill the whole page. The only problem is when I use an image instead of just selecting a color for the background of my website it makes the background of the blog posts transparent. I would like to know if there is a way to make that background of the blog posts a solid color. I’ve tried altering the coding a few times but I’m new to WordPress so I’m sure it’s just something I’m not doing properly. If anyone can help me please let me know! The URL to our website is https://www.hiddenhungerinternational.org if you would to see what the issue is in more detail.