Change the color to the background

Site URL: http://www.thebridgesfoundation.info/coquille-tidal-wetland-conservation-project

Hello, We have a text box on our page where we want to change the background color to make it stand out. I emailed support and was told it was an advanced feature and had to come to the forum. I am hoping someone can help. 

We have added a password to the URL. The password is "help". 

Here is the box we want to change the color for: 

Add to Design > Custom CSS

div#page-629288dea0e4730531e61dfb>.row>.span-5 {
    background-color: green;
}